MECHANISMS OF LABOR
OCCIPUT ANTERIOR PRESENTATION
CHARACTERISTICS OF NORMAL LABOR
FIRST STAGE OF LABOR
SECOND STAGE OF LABOR
MANAGEMENT OF NORMAL LABOR
MANAGEMENT OF THE FIRST STAGE OF LABOR
MANAGEMENT OF THE SECOND STAGE OF LABOR
LABOR MANAGEMENT PROTOCOLS
Labor is the process that leads to childbirth. It begins with the onset of regular uterine contractions and ends with delivery of the newborn and expulsion of the placenta. The term labor in the obstetrical context takes on several connotations from the English language. It is undoubtedly true that pregnancy and birth are physiological processes, and as such, labor and delivery should be considered to be normal for most women (Lawrence, 2012). This understanding of normal labor and delivery as a physiological process has come under some scrutiny in the past decade because pelvic floor disorders have been observed to be more prevalent among women who have delivered at least one child (Handa, 2011; Nygaard, 2008). Determining which aspects of childbirth contribute most to this risk has become an area of intense investigation and discussed further in Chapter 30 (p. 588).
MECHANISMS OF LABOR
At the onset of labor, the position of the fetus with respect to the birth canal is critical to the route of delivery and thus should be determined in early labor. Important relationships include fetal lie, presentation, attitude, and position.
The relation of the fetal long axis to that of the mother is termed fetal lie and is either longitudinal or transverse. Occasionally, the fetal and the maternal axes may cross at a 45-degree angle, forming an oblique lie. This lie is unstable and becomes longitudinal or transverse during labor. A longitudinal lie is present in more than 99 percent of labors at term. Predisposing factors for transverse fetal position include multiparity, placenta previa, hydramnios, and uterine anomalies (Chap. 23, p. 468).
The presenting part is that portion of the fetal body that is either foremost within the birth canal or in closest proximity to it. It typically can be felt through the cervix on vaginal examination. Accordingly, in longitudinal lies, the presenting part is either the fetal head or breech, creating cephalic and breech presentations, respectively. When the fetus lies with the long axis transversely, the shoulder is the presenting part. Table 22-1 describes the incidences of the various fetal presentations.
TABLE 22-1. Fetal Presentation in 68,097 Singleton Pregnancies at Parkland Hospital
Such presentations are classified according to the relationship between the head and body of the fetus (Fig. 22-1). Ordinarily, the head is flexed sharply so that the chin is in contact with the thorax. The occipital fontanel is the presenting part, and this presentation is referred to as a vertex or occiput presentation. Much less commonly, the fetal neck may be sharply extended so that the occiput and back come in contact, and the face is foremost in the birth canal—face presentation (Fig. 23-6, p. 466). The fetal head may assume a position between these extremes, partially flexed in some cases, with the anterior (large) fontanel, or bregma, presenting—sinciput presentation—or partially extended in other cases, to have a brow presentation (Fig. 23-8, p. 468). These latter two presentations are usually transient. As labor progresses, sinciput and brow presentations almost always convert into vertex or face presentations by neck flexion or extension, respectively. Failure to do so can lead to dystocia, as discussed in Chapter 23 (p. 455).
Figure 22-1 Longitudinal lie. Cephalic presentation. Differences in attitude of the fetal body in (A) vertex, (B) sinciput, (C) brow, and (D) face presentations. Note changes in fetal attitude in relation to fetal vertex as the fetal head becomes less flexed.
The term fetus usually presents with the vertex, most logically because the uterus is piriform or pear shaped. Although the fetal head at term is slightly larger than the breech, the entire podalic pole of the fetus—that is, the breech and its flexed extremities—is bulkier and more mobile than the cephalic pole. The cephalic pole is composed of the fetal head only. Until approximately 32 weeks, the amnionic cavity is large compared with the fetal mass, and the fetus is not crowded by the uterine walls. Subsequently, however, the ratio of amnionic fluid volume decreases relative to the increasing fetal mass. As a result, the uterine walls are apposed more closely to the fetal parts.
If presenting by the breech, the fetus often changes polarity to make use of the roomier fundus for its bulkier and more mobile podalic pole. As discussed in Chapter 28 (p. 559), the incidence of breech presentation decreases with gestational age. It approximates 25 percent at 28 weeks, 17 percent at 30 weeks, 11 percent at 32 weeks, and then decreases to approximately 3 percent at term. The high incidence of breech presentation in hydrocephalic fetuses is in accord with this theory, as the larger fetal cephalic pole requires more room than its podalic pole.
When the fetus presents as a breech, the three general configurations are frank, complete, and footling presentations and are described in Chapter 28 (p. 559). Breech presentation may result from circumstances that prevent normal version from taking place. One example is a septum that protrudes into the uterine cavity (Chap. 3, p. 42). A peculiarity of fetal attitude, particularly extension of the vertebral column as seen in frank breeches, also may prevent the fetus from turning. If the placenta is implanted in the lower uterine segment, it may distort normal intrauterine anatomy and result in a breech presentation.
Fetal Attitude or Posture
In the later months of pregnancy, the fetus assumes a characteristic posture described as attitude or habitus as shown in Figure 22-1. As a rule, the fetus forms an ovoid mass that corresponds roughly to the shape of the uterine cavity. The fetus becomes folded or bent upon itself in such a manner that the back becomes markedly convex; the head is sharply flexed so that the chin is almost in contact with the chest; the thighs are flexed over the abdomen; and the legs are bent at the knees. In all cephalic presentations, the arms are usually crossed over the thorax or become parallel to the sides. The umbilical cord lies in the space between them and the lower extremities. This characteristic posture results from the mode of fetal growth and its accommodation to the uterine cavity.
Abnormal exceptions to this attitude occur as the fetal head becomes progressively more extended from the vertex to the face presentation (see Fig. 22-1). This results in a progressive change in fetal attitude from a convex (flexed) to a concave (extended) contour of the vertebral column.
Position refers to the relationship of an arbitrarily chosen portion of the fetal presenting part to the right or left side of the birth canal. Accordingly, with each presentation there may be two positions—right or left. The fetal occiput, chin (mentum), and sacrum are the determining points in vertex, face, and breech presentations, respectively (Figs. 22-2 to 22-6). Because the presenting part may be in either the left or right position, there are left and right occipital, left and right mental, and left and right sacral presentations. These are abbreviated as LO and RO, LM and RM, and LS and RS, respectively.
FIGURE 22-2 Longitudinal lie. Vertex presentation. A. Left occiput anterior (LOA). B. Left occiput posterior (LOP).
FIGURE 22-3 Longitudinal lie. Vertex presentation. A. Right occiput posterior (ROP). B. Right occiput transverse (ROT).
FIGURE 22-4 Longitudinal lie. Vertex presentation. Right occiput anterior (ROA).
FIGURE 22-5 Longitudinal lie. Face presentation. Left and right mentum anterior and right mentum posterior positions.
FIGURE 22-6 Longitudinal lie. Breech presentation. Left sacrum posterior (LSP).
Varieties of Presentations and Positions
For still more accurate orientation, the relationship of a given portion of the presenting part to the anterior, transverse, or posterior portion of the maternal pelvis is considered. Because the presenting part in right or left positions may be directed anteriorly (A), transversely (T), or posteriorly (P), there are six varieties of each of the three presentations as shown in Figures 22-2 to 22-6. Thus, in an occiput presentation, the presentation, position, and variety may be abbreviated in clockwise fashion as:
Approximately two thirds of all vertex presentations are in the left occiput position, and one third in the right.
In shoulder presentations, the acromion (scapula) is the portion of the fetus arbitrarily chosen for orientation with the maternal pelvis. One example of the terminology sometimes employed for this purpose is illustrated in Figure 22-7. The acromion or back of the fetus may be directed either posteriorly or anteriorly and superiorly or inferiorly. Because it is impossible to differentiate exactly the several varieties of shoulder presentation by clinical examination and because such specific differentiation serves no practical purpose, it is customary to refer to all transverse lies simply as shoulder presentations. Another term used is transverse lie, with back up or back down, which is clinically important when deciding incision type for cesarean delivery (Chap. 23, p. 468).
FIGURE 22-7 Transverse lie. Right acromiodorsoposterior (RADP). The shoulder of the fetus is to the mother’s right, and the back is posterior.
Diagnosis of Fetal Presentation and Position
Several methods can be used to diagnose fetal presentation and position. These include abdominal palpation, vaginal examination, auscultation, and, in certain doubtful cases, sonography. Rarely, plain radiographs, computed tomography, or magnetic resonance imaging may be used.
Abdominal Palpation—Leopold Maneuvers
Abdominal examination can be conducted systematically employing the four maneuvers described by Leopold in 1894 and shown in Figure 22-8. The mother lies supine and comfortably positioned with her abdomen bared. These maneuvers may be difficult if not impossible to perform and interpret if the patient is obese, if there is excessive amnionic fluid, or if the placenta is anteriorly implanted.
FIGURE 22-8 Leopold maneuvers (A–D) performed in a fetus with a longitudinal lie in the left occiput anterior position (LOA).
The first maneuver permits identification of which fetal pole—that is, cephalic or podalic—occupies the uterine fundus. The breech gives the sensation of a large, nodular mass, whereas the head feels hard and round and is more mobile and ballottable.
Performed after determination of fetal lie, the second maneuver is accomplished as the palms are placed on either side of the maternal abdomen, and gentle but deep pressure is exerted. On one side, a hard, resistant structure is felt—the back. On the other, numerous small, irregular, mobile parts are felt—the fetal extremities. By noting whether the back is directed anteriorly, transversely, or posteriorly, fetal orientation can be determined.
The third maneuver is performed by grasping with the thumb and fingers of one hand the lower portion of the maternal abdomen just above the symphysis pubis. If the presenting part is not engaged, a movable mass will be felt, usually the head. The differentiation between head and breech is made as in the first maneuver. If the presenting part is deeply engaged, however, the findings from this maneuver are simply indicative that the lower fetal pole is in the pelvis, and details are then defined by the fourth maneuver.
To perform the fourth maneuver, the examiner faces the mother’s feet and, with the tips of the first three fingers of each hand, exerts deep pressure in the direction of the axis of the pelvic inlet. In many instances, when the head has descended into the pelvis, the anterior shoulder may be differentiated readily by the third maneuver.
Abdominal palpation can be performed throughout the latter months of pregnancy and during and between the contractions of labor. With experience, it is possible to estimate the size of the fetus. According to Lydon-Rochelle and colleagues (1993), experienced clinicians accurately identify fetal malpresentation using Leopold maneuvers with a high sensitivity—88 percent, specificity—94 percent, positive-predictive value—74 percent, and negative-predictive value—97 percent.
Before labor, the diagnosis of fetal presentation and position by vaginal examination is often inconclusive because the presenting part must be palpated through a closed cervix and lower uterine segment. With the onset of labor and after cervical dilatation, vertex presentations and their positions are recognized by palpation of the various fetal sutures and fontanels. Face and breech presentations are identified by palpation of facial features and fetal sacrum, respectively.
In attempting to determine presentation and position by vaginal examination, it is advisable to pursue a definite routine, comprising four movements. First, the examiner inserts two fingers into the vagina and the presenting part is found. Differentiation of vertex, face, and breech is then accomplished readily. Second, if the vertex is presenting, the fingers are directed posteriorly and then swept forward over the fetal head toward the maternal symphysis (Fig. 22-9). During this movement, the fingers necessarily cross the sagittal suture and its linear course is delineated. Next, the positions of the two fontanels are ascertained. For this, fingers are passed to the most anterior extension of the sagittal suture, and the fontanel encountered there is examined and identified. Then, with a sweeping motion, the fingers pass along the suture to the other end of the head until the other fontanel is felt and differentiated (Fig. 22-10). Last, the station, or extent to which the presenting part has descended into the pelvis, can also be established at this time (p. 449). Using these maneuvers, the various sutures and fontanels are located readily (Fig. 7-11, p. 139).
FIGURE 22-9 Locating the sagittal suture by vaginal examination.
FIGURE 22-10 Differentiating the fontanels by vaginal examination.
Sonography and Radiography
Sonographic techniques can aid fetal position identification, especially in obese women or in women with rigid abdominal walls. Zahalka and associates (2005) compared digital examinations with transvaginal and transabdominal sonography for fetal head position determination during second-stage labor and reported that transvaginal sonography was superior.
Occiput Anterior Presentation
In most cases, the vertex enters the pelvis with the sagittal suture lying in the transverse pelvic diameter. The fetus enters the pelvis in the left occiput transverse (LOT) position in 40 percent of labors and in the right occiput transverse (ROT) position in 20 percent (Caldwell, 1934). In occiput anterior positions—LOA or ROA—the head either enters the pelvis with the occiput rotated 45 degrees anteriorly from the transverse position, or this rotation occurs subsequently. The mechanism of labor in all these presentations is usually similar.
The positional changes of the presenting part required to navigate the pelvic canal constitute the mechanisms of labor. The cardinal movements of labor are engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion (Fig. 22-11). During labor, these movements not only are sequential but also show great temporal overlap. For example, as part of engagement, there is both flexion and descent of the head. It is impossible for the movements to be completed unless the presenting part descends simultaneously. Concomitantly, uterine contractions effect important modifications in fetal attitude, or habitus, especially after the head has descended into the pelvis. These changes consist principally of fetal straightening, with loss of dorsal convexity and closer application of the extremities to the body. As a result, the fetal ovoid is transformed into a cylinder, with the smallest possible cross section typically passing through the birth canal.
Figure 22-11 Cardinal movements of labor and delivery from a left occiput anterior position.
The mechanism by which the biparietal diameter—the greatest transverse diameter in an occiput presentation—passes through the pelvic inlet is designated engagement. The fetal head may engage during the last few weeks of pregnancy or not until after labor commencement. In many multiparous and some nulliparous women, the fetal head is freely movable above the pelvic inlet at labor onset. In this circumstance, the head is sometimes referred to as “floating.” A normal-sized head usually does not engage with its sagittal suture directed anteroposteriorly. Instead, the fetal head usually enters the pelvic inlet either transversely or obliquely. Segel and coworkers (2012) analyzed labor in 5341 nulliparous women and found that fetal head engagement before labor onset did not affect vaginal delivery rates in either spontaneous or induced labor.
Asynclitism. The fetal head tends to accommodate to the transverse axis of the pelvic inlet, whereas the sagittal suture, while remaining parallel to that axis, may not lie exactly midway between the symphysis and the sacral promontory. The sagittal suture frequently is deflected either posteriorly toward the promontory or anteriorly toward the symphysis (Fig. 22-12). Such lateral deflection to a more anterior or posterior position in the pelvis is called asynclitism. If the sagittal suture approaches the sacral promontory, more of the anterior parietal bone presents itself to the examining fingers, and the condition is called anterior asynclitism. If, however, the sagittal suture lies close to the symphysis, more of the posterior parietal bone will present, and the condition is called posterior asynclitism. With extreme posterior asynclitism, the posterior ear may be easily palpated.
FIGURE 22-12 Synclitism and asynclitism.
Moderate degrees of asynclitism are the rule in normal labor. However, if severe, the condition is a common reason for cephalopelvic disproportion even with an otherwise normal-sized pelvis. Successive shifting from posterior to anterior asynclitism aids descent.
This movement is the first requisite for birth of the newborn. In nulliparas, engagement may take place before the onset of labor, and further descent may not follow until the onset of the second stage. In multiparas, descent usually begins with engagement. Descent is brought about by one or more of four forces: (1) pressure of the amnionic fluid, (2) direct pressure of the fundus upon the breech with contractions, (3) bearing-down efforts of maternal abdominal muscles, and (4) extension and straightening of the fetal body.
As soon as the descending head meets resistance, whether from the cervix, pelvic walls, or pelvic floor, it normally flexes. With this movement, the chin is brought into more intimate contact with the fetal thorax, and the appreciably shorter suboccipitobregmatic diameter is substituted for the longer occipitofrontal diameter (Figs. 22-13 and 22-14).
FIGURE 22-13 Lever action produces flexion of the head. Conversion from occipitofrontal to suboccipitobregmatic diameter typically reduces the anteroposterior diameter from nearly 12 to 9.5 cm.
FIGURE 22-14 Four degrees of head flexion. The solid line represents the occipitomental diameter, whereas the broken line connects the center of the anterior fontanel with the posterior fontanel. A. Flexion poor. B. Flexion moderate. C. Flexion advanced. D. Flexion complete. Note that with complete flexion, the chin is on the chest. The suboccipitobregmatic diameter, the shortest anteroposterior diameter of the fetal head, is passing through the pelvic inlet.
This movement consists of a turning of the head in such a manner that the occiput gradually moves toward the symphysis pubis anteriorly from its original position or, less commonly, posteriorly toward the hollow of the sacrum (Figs. 22-15 to 22-17). Internal rotation is essential for completion of labor, except when the fetus is unusually small.
FIGURE 22-15 Mechanism of labor for the left occiput transverse position, lateral view. A. Engagement. B. After engagement, further descent. C. Descent and initial internal rotation. D. Rotation and extension.
FIGURE 22-16 Mechanism of labor for left occiput anterior position.
FIGURE 22-17 Mechanism of labor for right occiput posterior position showing anterior rotation.
Calkins (1939) studied more than 5000 women in labor to ascertain the time of internal rotation. He concluded that in approximately two thirds, internal rotation is completed by the time the head reaches the pelvic floor; in about another fourth, internal rotation is completed shortly after the head reaches the pelvic floor; and in the remaining 5 percent, rotation does not take place. When the head fails to turn until reaching the pelvic floor, it typically rotates during the next one or two contractions in multiparas. In nulliparas, rotation usually occurs during the next three to five contractions.
After internal rotation, the sharply flexed head reaches the vulva and undergoes extension. If the sharply flexed head, on reaching the pelvic floor, did not extend but was driven farther downward, it would impinge on the posterior portion of the perineum and would eventually be forced through the perineal tissues. When the head presses on the pelvic floor, however, two forces come into play. The first force, exerted by the uterus, acts more posteriorly, and the second, supplied by the resistant pelvic floor and the symphysis, acts more anteriorly. The resultant vector is in the direction of the vulvar opening, thereby causing head extension. This brings the base of the occiput into direct contact with the inferior margin of the symphysis pubis (see Fig. 22-16).
With progressive distention of the perineum and vaginal opening, an increasingly larger portion of the occiput gradually appears. The head is born as the occiput, bregma, forehead, nose, mouth, and finally the chin pass successively over the anterior margin of the perineum (see Fig. 22-17). Immediately after its delivery, the head drops downward so that the chin lies over the maternal anus.
The delivered head next undergoes restitution (see Fig. 22-11). If the occiput was originally directed toward the left, it rotates toward the left ischial tuberosity. If it was originally directed toward the right, the occiput rotates to the right. Restitution of the head to the oblique position is followed by external rotation completion to the transverse position. This movement corresponds to rotation of the fetal body and serves to bring its bisacromial diameter into relation with the anteroposterior diameter of the pelvic outlet. Thus, one shoulder is anterior behind the symphysis and the other is posterior. This movement apparently is brought about by the same pelvic factors that produced internal rotation of the head.
Almost immediately after external rotation, the anterior shoulder appears under the symphysis pubis, and the perineum soon becomes distended by the posterior shoulder. After delivery of the shoulders, the rest of the body quickly passes.
Occiput Posterior Presentation
In approximately 20 percent of labors, the fetus enters the pelvis in an occiput posterior (OP) position (Caldwell, 1934). The right occiput posterior (ROP) is slightly more common than the left (LOP). It appears likely from radiographic evidence that posterior positions are more often associated with a narrow forepelvis. They also are more commonly seen in association with anterior placentation (Gardberg, 1994a).
In most occiput posterior presentations, the mechanism of labor is identical to that observed in the transverse and anterior varieties, except that the occiput has to internally rotate to the symphysis pubis through 135 degrees, instead of 90 and 45 degrees, respectively (see Fig. 22-17).
Effective contractions, adequate head flexion, and average fetal size together permit most posteriorly positioned occiputs to rotate promptly as soon as they reach the pelvic floor, and labor is not lengthened appreciably. In perhaps 5 to 10 percent of cases, however, rotation may be incomplete or may not take place at all, especially if the fetus is large (Gardberg, 1994b). Poor contractions, faulty head flexion, or epidural analgesia, which diminishes abdominal muscular pushing and relaxes pelvic floor muscles, may predispose to incomplete rotation. If rotation is incomplete, transverse arrest may result. If no rotation toward the symphysis takes place, the occiput may remain in the direct occiput posterior position, a condition known as persistent occiput posterior. Both persistent occiput posterior and transverse arrest represent deviations from the normal mechanisms of labor and are considered further in Chapter 23.
Fetal Head Shape Changes
In vertex presentations, labor forces alter fetal head shape. In prolonged labors before complete cervical dilatation, the portion of the fetal scalp immediately over the cervical os becomes edematous (Fig. 33-1, p. 647). This swelling, known as the caput succedaneum, is shown in Figures 22-18 and 22-19. It usually attains a thickness of only a few millimeters, but in prolonged labors it may be sufficiently extensive to prevent differentiation of the various sutures and fontanels. More commonly, the caput is formed when the head is in the lower portion of the birth canal and frequently only after the resistance of a rigid vaginal outlet is encountered. Because it develops over the most dependent area of the head, one may deduce the original fetal head position by noting the location of the caput succedaneum.
FIGURE 22-18 Formation of caput succedaneum and head molding.
FIGURE 22-19 Considerable molding of the head and caput succedaneum formation in a recently delivered newborn.
In addition to soft tissue changes, the bony fetal head shape is also altered by external compressive forces and is referred to as molding (see Fig. 22-19). Possibly related to Braxton Hicks contractions, some molding develops before labor. Most studies indicate that there is seldom overlapping of the parietal bones. A “locking” mechanism at the coronal and lambdoidal connections actually prevents such overlapping (Carlan, 1991). Molding results in a shortened suboccipitobregmatic diameter and a lengthened mentovertical diameter. These changes are of greatest importance in women with contracted pelves or asynclitic presentations. In these circumstances, the degree to which the head is capable of molding may make the difference between spontaneous vaginal delivery and an operative delivery. Some older literature cited severe head molding as a cause for possible cerebral trauma. Because of the multitude of associated factors, for example, prolonged labor with fetal sepsis and acidosis, it is impossible to link molding to any alleged fetal or neonatal neurological sequelae. Most cases of molding resolve within the week following delivery, although persistent cases have been described (Graham, 2006).
CHARACTERISTICS OF NORMAL LABOR
The greatest impediment to understanding normal labor is recognizing its start. The strict definition of labor—uterine contractions that bring about demonstrable effacement and dilatation of the cervix—does not easily aid the clinician in determining when labor has actually begun, because this diagnosis is confirmed only retrospectively. Several methods may be used to define its start. One defines onset as the clock time when painful contractions become regular. Unfortunately, uterine activity that causes discomfort, but that does not represent true labor, may develop at any time during pregnancy. False labor often stops spontaneously, or it may proceed rapidly into effective contractions.
A second method defines the onset of labor as beginning at the time of admission to the labor unit. In the United States, admission for labor is frequently based on the extent of cervical dilatation accompanied by painful contractions. If a woman has intact membranes, then a cervical dilatation of 3 to 4 cm or greater is presumed to be a reasonably reliable threshold for the diagnosis of labor. In this case, labor onset commences with the time of admission. This presumptive method obviates many of the uncertainties in diagnosing labor during earlier stages of cervical dilatation. Laughon and colleagues (2012) compared the duration of spontaneous labor at term in nulliparas delivered in the United States between 1959 and 1966 to that of those delivered from 2002 to 2008. As shown in Figure 22-20, the length of labor increased by approximately 2 hours during those 50 years.
FIGURE 22-20 Average labor curves for women with singleton term pregnancies presenting in spontaneous labor with vaginal delivery for nulliparas for 1959–1966 compared with 2002–2008. (From Zhang, 2002.)
First Stage of Labor
Assuming that the diagnosis has been confirmed, what then are the expectations for the progress of normal labor? A scientific approach was begun by Friedman (1954), who described a characteristic sigmoid pattern for labor by graphing cervical dilatation against time. This graphical approach, based on statistical observations, changed labor management. Friedman developed the concept of three functional labor divisions to describe the physiological objectives of each division as shown in Figure 22-21. First, during the preparatory division, although the cervix dilates little, its connective tissue components change considerably (Chap. 21, p. 410). Sedation and conduction analgesia are capable of arresting this labor division. The dilatational division, during which dilatation proceeds at its most rapid rate, is unaffected by sedation. Last, the pelvic division commences with the deceleration phase of cervical dilatation. The classic labor mechanisms that involve the cardinal fetal movements of the cephalic presentation take place principally during this pelvic division. In actual practice, however, the onset of the pelvic division is seldom clearly identifiable.
FIGURE 22-21 Labor course divided functionally on the basis of dilatation and descent curves into: (1) a preparatory division, including latent and acceleration phases; (2) a dilatational division, occupying the phase of maximum slope; and (3) a pelvic division, encompassing both deceleration phase and second stage concurrent with the phase of maximum slope of descent. (Redrawn from Friedman, 1978.)
As shown in Figure 22-21, the pattern of cervical dilatation during the preparatory and dilatational divisions of normal labor is a sigmoid curve. Two phases of cervical dilatation are defined. The latent phasecorresponds to the preparatory division, and the active phase to the dilatational division. And as shown in Figure 22-22, Friedman subdivided the active phase into the acceleration phase, the phase of maximum slope, and the deceleration phase.
FIGURE 22-22 Composite of the average dilatation curve for nulliparous labor. The first stage is divided into a relatively flat latent phase and a rapidly progressive active phase. In the active phase, there are three identifiable component parts that include an acceleration phase, a phase of maximum slope, and a deceleration phase. (Redrawn from Friedman, 1978.)
The onset of latent labor, as defined by Friedman (1972), is the point at which the mother perceives regular contractions. The latent phase for most women ends once dilatation of 3 to 5 cm is achieved. This threshold may be clinically useful, for it defines dilatation limits beyond which active labor can be expected.
This concept of a latent phase has great significance in understanding normal human labor, because labor is considerably longer when a latent phase is included. To better illustrate this, Figure 22-23 shows eight labor curves from nulliparas in whom labor was diagnosed beginning with their admission, rather than with the onset of regular contractions. When labor is defined similarly, there is remarkable similarity of individual labor curves.
FIGURE 22-23 Progress of labor in primigravid women from the time of admission. When the starting point on the abscissa begins with admission to the hospital, a latent phase is not observed.
Prolonged Latent Phase. Friedman and Sachtleben (1963) defined this by a latent phase exceeding 20 hours in the nullipara and 14 hours in the multipara. These times corresponded to the 95th percentiles. Factors that affected latent phase duration include excessive sedation or epidural analgesia; unfavorable cervical condition, that is, thick, uneffaced, or undilated; and false labor. In those who had been administered heavy sedation, 85 percent of women eventually entered active labor. In another 10 percent, uterine contractions ceased, suggesting that they had false labor. The remaining 5 percent experienced persistence of an abnormal latent phase and required oxytocin stimulation. Amniotomy was discouraged because of the 10-percent incidence of false labor. Sokol and associates (1977) reported a 3- to 4- percent incidence of prolonged latent phase, regardless of parity. Friedman (1972) reported that latent phase prolongation did not adversely influence fetal or maternal morbidity or mortality rates. However, Chelmow and coworkers (1993) disputed the long-held belief that prolongation of the latent phase is benign.
The progress of labor in nulliparas has particular significance because these curves all reveal a rapid change in the slope of cervical dilatation rates between 3 and 5 cm (see Fig. 22-23). Thus, cervical dilatation of 3 to 5 cm or more, in the presence of uterine contractions, can be taken to reliably represent the threshold for active labor. Similarly, these curves provide useful guideposts for labor management.
Turning again to Friedman (1955), the mean duration of active-phase labor in nulliparas was 4.9 hours. But the standard deviation of 3.4 hours is large, hence, the active phase was reported to have a statistical maximum of 11.7 hours. Indeed, rates of cervical dilatation ranged from a minimum of 1.2 up to 6.8 cm/hr. Friedman (1972) also found that multiparas progress somewhat faster in active-phase labor, with a minimum normal rate of 1.5 cm/hr. His analysis of active-phase labor concomitantly describes rates of fetal descent and cervical dilatation (see Fig. 22-21). Descent begins in the later stage of active dilatation, commencing at 7 to 8 cm in nulliparas and becoming most rapid after 8 cm.
Active-Phase Abnormalities. These have bee reported to occur in 25 percent of nulliparous and 15 percent of multiparous labors (Sokol, 1977). Friedman (1972) subdivided active-phase problems into protraction and arrest disorders. Protraction is defined as a slow rate of cervical dilatation or descent, which for nulliparas was < 1.2 cm dilatation per hour or < 1 cm descent per hour. For multiparas, protraction was defined as < 1.5 cm dilatation per hour or < 2 cm descent per hour. Friedman defined arrest as a complete cessation of dilatation or descent. Arrest of dilatation was defined as 2 hours with no cervical change, and arrest of descent as 1 hour without fetal descent. The prognosis for protraction and arrest disorders differs considerably. Friedman found that approximately 30 percent of women with protraction disorders had cephalopelvic disproportion (CPD). This compared with a 45-percent CPD rate for women in whom an arrest disorder developed. Abnormal labor patterns, diagnostic criteria, and treatment methods are summarized in Chapter 23 (p. 456).
Hendricks and colleagues (1970) challenged Friedman’s conclusions about the course of normal human labor. Their principal differences included: (1) absence of a latent phase, (2) no deceleration phase, (3) brevity of labor, and (4) dilatation at similar rates for nulliparas and multiparas after 4 cm. They disputed the concept of a latent phase because they observed that the cervix dilated and effaced slowly during the 4 weeks preceding labor. They contended that the latent phase actually progressed over several weeks. They also reported that labor was relatively rapid. Specifically, the average time from admission to complete dilatation was 4.8 hours for nulliparas and 3.2 hours for multiparas.
There have been other reports in which investigators have reassessed the Friedman labor curves. Zhang and associates (2010) studied electronic labor records from 62,415 parturients with spontaneous labor at term and vaginal birth. They found that normal labor may take more than 6 hours to progress from 4 to 5 cm and more than 3 hours to progress from 5 to 6 cm dilation. Thereafter, labor accelerated much faster in multiparas. In a study performed at Parkland Hospital, epidural analgesia was found to lengthen the active phase of the Friedman labor curve by 1 hour (Alexander, 2002). This increase was the result of a slight but significant decrease in the rate of cervical dilatation—1.4 cm/hr in women given epidural analgesia compared with 1.6 cm/hr in those without such analgesia. There are now several reports that maternal obesity lengthens the first stages of labor by 30 to 60 minutes (Chin, 2012; Kominiarek, 2011). Finally, Adams and coworkers (2012) found that maternal fear increased labor by approximately 45 minutes.
Second Stage of Labor
This stage begins with complete cervical dilatation and ends with fetal delivery. The median duration is approximately 50 minutes for nulliparas and about 20 minutes for multiparas, but it is highly variable (Kilpatrick, 1989). In a woman of higher parity with a previously dilated vagina and perineum, two or three expulsive efforts after full cervical dilatation may suffice to complete delivery. Conversely, in a woman with a contracted pelvis, with a large fetus, or with impaired expulsive efforts from conduction analgesia or sedation, the second stage may become abnormally long. Robinson and colleagues (2011) found that increasing maternal body mass index did not interfere with the second stage of labor. Abnormalities of this labor stage are described in Chapter 23 (p. 456).
Duration of Labor
Our understanding of the normal duration of labor may be clouded by the many clinical variables that affect conduct of labor in modern obstetrical units. Kilpatrick and Laros (1989) reported that the mean length of first- and second-stage labor was approximately 9 hours in nulliparous women without regional analgesia, and that the 95th percentile upper limit was 18.5 hours. Corresponding times for multiparous women were a mean of 6 hours with a 95th percentile maximum of 13.5 hours. These authors defined labor onset as the time when a woman recalled regular, painful contractions every 3 to 5 minutes that led to cervical change.
Spontaneous labor was analyzed in nearly 25,000 women delivered at term at Parkland Hospital in the early 1990s. Almost 80 percent of women were admitted with a cervical dilatation of 5 cm or less. Parity—nulliparous versus multiparous—and cervical dilatation at admission were significant determinants of the length of spontaneous labor. The median time from admission to spontaneous delivery for all parturients was 3.5 hours, and 95 percent of all women delivered within 10.1 hours. These results suggest that normal human labor is relatively short. Zhang and associates (2009a,b) described similar findings in their study of 126,887 deliveries from 12 United States institutions.
Summary of Normal Labor
Labor is characterized by brevity and considerable biological variation. Active labor can be reliably diagnosed when cervical dilatation is 3 cm or more in the presence of uterine contractions. Once this cervical dilatation threshold is reached, normal progression to delivery can be expected, depending on parity, in the ensuing 4 to 6 hours. Anticipated progress during a 1- to 2-hour second stage is monitored to ensure fetal safety. Finally, most women in spontaneous labor, regardless of parity, if left unaided, will deliver within approximately 10 hours after admission for spontaneous labor. Insufficient uterine activity is a common and correctable cause of abnormal labor progress. Therefore, when the length of otherwise normal labor exceeds the expected norm, interventions other than cesarean delivery—for example, oxytocin administration—must be first considered.
MANAGEMENT OF NORMAL LABOR
The ideal management of labor and delivery requires two potentially opposing viewpoints on the part of clinicians. First, birthing should be recognized as a normal physiological process that most women experience without complications. Second, intrapartum complications, often arising quickly and unexpectedly, should be anticipated. Thus, clinicians must simultaneously make every woman and her supporters feel comfortable, yet ensure safety for the mother and newborn should complications suddenly develop. Principles such as these are the basis for a recent “Call to Action” by seven national organizations intended to emphasize quality patient care in labor and delivery (Lawrence, 2012). The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (2012) have collaborated in the development of Guidelines for Perinatal Care. These provide detailed information on the appropriate content of intrapartum care, including both personnel and facility requirements. Shown in Table 22-2 are the recommended nurse-to-patient ratios recommended for labor and delivery. Shown in Table 22-3 are the recommended room dimensions for these functions.
TABLE 22-2. Recommended Nurse/Patient Ratios for Labor and Delivery
TABLE 22-3. Recommended Minimum Room Dimensions for Labor and Delivery
Pregnant women should be urged to report early in labor rather than to procrastinate until delivery is imminent for fear that they might be experiencing false labor. Early admittance to the labor and delivery unit is important, especially if during antepartum care the woman, her fetus, or both have been identified as being at risk.
Identification of Labor
Although the differentiation between false and true labor is difficult at times, the diagnosis usually can be clarified by contraction frequency and intensity and by cervical dilatation. In those instances when a diagnosis of labor cannot be established with certainty, observation for a longer period is often wise.
Pates and associates (2007) studied the commonly used recommendations given to pregnant women that, in the absence of ruptured membranes or bleeding, uterine contractions 5 minutes apart for 1 hour—that is, ≥ 12 contractions in 1 hour—may signify labor onset. Among 768 women studied at Parkland Hospital, active labor defined as cervical dilatation ≥ 4 cm was diagnosed within 24 hours in three fourths of women with ≥ 12 contractions per hour. Bailit and coworkers (2005) compared labor outcomes of 6121 women who presented in active labor defined as uterine contractions plus cervical dilatation ≥ 4 cm with those of 2697 women who presented in the latent phase. Women admitted during latent-phase labor had more active-phase arrest, more frequent need for oxytocin labor stimulation, and higher rates of chorioamnionitis. It was concluded that physician interventions in women presenting in the latent phase may have been the cause of subsequent labor abnormalities.
Emergency Medical Treatment and Labor Act—EMTALA
Congress enacted EMTALA in 1986 to ensure public access to emergency services regardless of the ability to pay. All Medicare-participating hospitals with emergency services must provide an appropriate screening examination for any pregnant woman experiencing contractions and presenting to the emergency department for evaluation.
The definition of an emergency condition makes specific reference to a pregnant woman who is having contractions. Labor is defined as “the process of childbirth beginning with the latent phase of labor continuing through delivery of the placenta. A woman experiencing contractions is in true labor unless a physician certifies that after a reasonable time of observation the woman is in false labor.” A woman in true labor is considered “unstable” for interhospital transfer purposes until the newborn and placenta are delivered. An unstable woman may, however, be transferred at the direction of the patient or by a physician who certifies that the benefits of treatment at another facility outweigh the transfer risks. Physicians and hospitals violating these federal requirements are subject to civil penalties up to $50,000 and termination from the Medicare program.
Electronic Fetal Heart Rate Monitoring
As discussed in Chapter 24 (p. 473), electronic fetal heart rate monitoring is routinely used for high-risk pregnancies commencing at admission. Some investigators recommend monitoring women with low-risk pregnancies upon admission as a test of fetal well-being—the so-called fetal admission test. If no fetal heart rate abnormalities are detected, continuous electronic monitoring is replaced by intermittent assessment for the remainder of labor. We are of the view that electronic fetal heart rate monitoring is reasonable in the preadmission evaluation of women, including those who subsequently are discharged. At Parkland Hospital, external electronic monitoring is performed for at least 1 hour before discharging the woman who was ascertained to have false labor.
A major emphasis of obstetrical care during the 20th century was the movement to birthing in hospitals rather than in homes. In 2006, 98.9 percent of births in the United States took place in hospitals (Martin, 2011). Of the other 1.1 percent, 67.2 percent were in homes, and 27.6 percent were in birthing centers. Between 2004 and 2008, more than half of all states had an increase in home births (MacDorman, 2011). As discussed in Chapter 1 (p. 11) most studies suggest increased risks with home deliveries (Berghella, 2008; Cheng, 2013; de Jonge, 2013; Grunebaum, 2013). Indeed, Chervenak and colleagues (2013) have questioned the ethics of physicians voluntarily involved in home births.
Maternal blood pressure, temperature, pulse, and respiratory rate are recorded. The pregnancy record is promptly reviewed to identify complications. Problems identified or anticipated during prenatal care should be displayed prominently in the pregnancy record. Most often, unless there has been bleeding in excess of bloody show, a vaginal examination is performed. The gloved index and second fingers are then introduced into the vagina while avoiding the anal region (Fig. 22-24). The number of vaginal examinations correlates with infection-related morbidity, especially in cases of early membrane rupture.
FIGURE 22-24 To perform vaginal examination, the labia have been separated with one hand, and the first and second fingers of the other hand are carefully inserted into the introitus.
The woman should be instructed during the antepartum period to be aware of fluid leakage from the vagina and to report such an event promptly. Rupture of the membranes is significant for three reasons. First, if the presenting part is not fixed in the pelvis, the possibility of umbilical cord prolapse and compression is greatly increased. Second, labor is likely to begin soon if the pregnancy is at or near term. Third, if delivery is delayed after membrane rupture, intrauterine infection is more likely as the time interval increases (Herbst, 2007).
Upon sterile speculum examination, ruptured membranes are diagnosed if amnionic fluid pools in the posterior fornix or clear fluid flows from the cervical canal. Although several diagnostic tests for the detection of ruptured membranes have been recommended, none is completely reliable. If the diagnosis remains uncertain, another method involves pH determination of vaginal fluid. The pH of vaginal secretions normally ranges from 4.5 to 5.5, whereas that of amnionic fluid is usually 7.0 to 7.5. The use of the indicator nitrazine to identify ruptured membranes is a simple and fairly reliable method. Test papers are impregnated with the dye, and the color of the reaction between these paper strips and vaginal fluids is interpreted by comparison with a standard color chart. A pH above 6.5 is consistent with ruptured membranes. False-positive test results may occur with coexistent blood, semen, or bacterial vaginosis, whereas false-negative tests may result with scant fluid.
Other tests include arborization or ferning of vaginal fluid, which suggests amnionic rather than cervical fluid. Amnionic fluid crystallizes to form a fernlike pattern due to its relative concentrations of sodium chloride, proteins, and carbohydrates (Fig. 4-2, p. 49). Detection of alpha-fetoprotein in the vaginal vault has been used to identify amnionic fluid (Yamada, 1998). Although rarely required, identification may also follow injection of indigo carmine into the amnionic sac via abdominal amniocentesis.
The degree of cervical effacement usually is expressed in terms of the length of the cervical canal compared with that of an uneffaced cervix. When the length of the cervix is reduced by one half, it is 50-percent effaced. When the cervix becomes as thin as the adjacent lower uterine segment, it is completely, or 100-percent, effaced.
Cervical dilatation is determined by estimating the average diameter of the cervical opening by sweeping the examining finger from the margin of the cervical opening on one side to that on the opposite side. The diameter traversed is estimated in centimeters. The cervix is said to be dilated fully when the diameter measures 10 cm, because the presenting part of a term-size newborn usually can pass through a cervix this widely dilated.
The position of the cervix is determined by the relationship of the cervical os to the fetal head and is categorized as posterior, mid-position, or anterior. Along with position, the consistency of cervix is determined to be soft, firm, or intermediate between these two.
The level—or station—of the presenting fetal part in the birth canal is described in relationship to the ischial spines, which are halfway between the pelvic inlet and the pelvic outlet. When the lowermost portion of the presenting fetal part is at the level of the spines, it is designated as being at zero (0) station. In the past, the long axis of the birth canal above and below the ischial spines was arbitrarily divided into thirds by some and into fifths (approximately 1 cm) by other groups. In 1989, the American College of Obstetricians and Gynecologists adopted the classification of station that divides the pelvis above and below the spines into fifths. Each fifth represents 1 cm above or below the spines. Thus, as the presenting fetal part descends from the inlet toward the ischial spines, the designation is –5, –4, –3, –2, –1, then 0 station. Below the spines, as the presenting fetal part descends, it passes +1, +2, +3, +4, and +5 stations to delivery. Station +5 cm corresponds to the fetal head being visible at the introitus.
If the leading part of the fetal head is at 0 station or below, most often the fetal head has engaged—thus, the biparietal plane has passed through the pelvic inlet. If the head is unusually molded or if there is an extensive caput formation or both, engagement might not have taken place although the head appears to be at 0 station.
In a study done at five teaching centers in Denver, residents, nurses, and faculty were surveyed to determine what definitions were being used to describe fetal station (Carollo, 2004). Four different definitions were in use. Disturbingly, these investigators found that few caregivers were aware that others were using different definitions of station! Dupuis and colleagues (2005) tested the reliability of clinical estimations of station using the position of the leading part in centimeters above or below the spines as recommended by the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (2012). A birth simulator was used in which station could be precisely measured and compared with the vaginal examination done by clinicians. They reported that the clinical examiners were incorrect a third of the time.
These five characteristics: cervical dilatation, effacement, consistency, position, and fetal station are assessed when tabulating the Bishop score. This score is commonly used to predict labor induction outcome and is discussed in Chapter 26 (p. 526).
When a woman is admitted in labor, most often the hematocrit or hemoglobin concentration should be rechecked. The hematocrit can be measured easily and quickly. At Parkland Hospital, blood is collected in a standard collection tube with anticoagulant. From this, a heparinized capillary tube is filled to spin in a microhematocrit centrifuge in the labor and delivery unit. This provides a hematocrit value within 3 minutes. The initial collection tube is also sent to the hematology laboratory for evaluation. Another labeled tube of blood is allowed to clot and sent to the blood bank for blood type and antibody screen, if needed. A final sample is collected for syphilis and human immunodeficiency virus (HIV) serology. We obtain a urine specimen for protein determination in hypertensive women only (Chap. 40, p. 729). In some labor units, however, a clean-catch voided specimen is examined in all women for protein and glucose.
Women who have had no prenatal care should be considered to be at risk for syphilis, hepatitis B, and HIV (Chap. 65, p. 1265). In those with no prior prenatal care, these laboratory studies, as well as a blood type and antibody screen, should be performed (American Academy of Pediatrics and American College of Obstetricians and Gynecologists, 2012). Some states, for example, Texas, require routine testing for syphilis, hepatitis B, and HIV in all women admitted to labor and delivery units, even if these were done during prenatal care.
Management of the First Stage of Labor
As soon as possible after admittance, the remainder of a general examination is completed. Whether a pregnancy is normal can best be determined when all examinations, including record and laboratory review, are completed. A rational plan for monitoring labor can then be established based on the needs of the fetus and the mother. Because there are marked individual variations in labor lengths, precise statements as to its anticipated duration are unwise.
Intrapartum Fetal Monitoring
This is discussed in detail in Chapter 24. Briefly, the American Academy of Pediatrics and American College of Obstetricians and Gynecologists (2012) recommend that during first-stage labor, in the absence of any abnormalities, the fetal heart rate should be checked immediately after a contraction at least every 30 minutes and then every 15 minutes during the second stage. If continuous electronic monitoring is used, the tracing is evaluated at least every 30 minutes during the first stage and at least every 15 minutes during second-stage labor. For women with pregnancies at risk, fetal heart auscultation is performed at least every 15 minutes during first-stage labor and every 5 minutes during the second stage. Continuous electronic monitoring may be used with evaluation of the tracing every 15 minutes during the first stage of labor, and every 5 minutes during the second stage.
Although usually assessed by electronic monitoring as also discussed in Chapter 24, contractions can be both quantitatively and qualitatively evaluated manually. With the palm of the hand resting lightly on the uterus, the time of contraction onset is determined. Its intensity is gauged from the degree of firmness the uterus achieves. At the acme of effective contractions, the finger or thumb cannot readily indent the uterus during a “firm” contraction. The time at which the contraction disappears is noted next. This sequence is repeated to evaluate the frequency, duration, and intensity of uterine contractions.
Maternal Vital Signs
Temperature, pulse, and blood pressure are evaluated at least every 4 hours. If membranes have been ruptured for many hours before labor onset or if there is a borderline temperature elevation, the temperature is checked hourly. Moreover, with prolonged membrane rupture, defined as greater than 18 hours, antimicrobial administration for prevention of group B streptococcal infections is recommended. This is discussed in Chapter 64 (p. 1249).
Subsequent Cervical Examinations
During the first stage of labor, the need for subsequent vaginal examinations to monitor cervical change and presenting part position will vary considerably. When the membranes rupture, an examination to exclude cord prolapse should be performed expeditiously if the fetal head was not definitely engaged at the previous examination. The fetal heart rate should also be checked immediately and during the next uterine contraction to help detect occult umbilical cord compression. At Parkland Hospital, periodic pelvic examinations are typically performed at 2- to 3-hour intervals to evaluate labor progress.
Food should be withheld during active labor and delivery. Gastric emptying time is remarkably prolonged once labor is established and analgesics are administered. As a consequence, ingested food and most medications remain in the stomach and are not absorbed. Instead, they may be vomited and aspirated (Chap. 25, p. 519). According to the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (2007), sips of clear liquids, occasional ice chips, and lip moisturizers are permitted.
Although it has become customary in many hospitals to establish an intravenous infusion system routinely early in labor, there is seldom any real need for this in the normal pregnant woman, at least until analgesia is administered. An intravenous infusion system is advantageous during the immediate puerperium to administer oxytocin prophylactically and at times therapeutically when uterine atony persists. Moreover, with longer labors, the administration of glucose, sodium, and water to the otherwise fasting woman at the rate of 60 to 120 mL/hr prevents dehydration and acidosis. Shrivastava and associates (2009) noted shorter labors in nulliparas delivering vaginally who were provided an intravenous normal saline with dextrose solution compared with those given saline solution only. Garite and coworkers (2000) randomly assigned 195 women in labor to receive either 125 or 250 mL/hr of lactated Ringer or isotonic sodium chloride solution. The mean volume of total intravenous fluid was 2008 mL in the 125 mL/hr group and 2487 mL in the 250 mL/hr group. Labor lasted > 12 hours in significantly more (26 versus 13 percent) of the women given a 125 mL/hr infusion compared with those given 250 mL/hr—26 versus 13 percent, respectively.
The normal laboring woman need not be confined to bed early in labor. A comfortable chair may be beneficial psychologically and perhaps physiologically. In bed, the laboring woman should be allowed to assume the position she finds most comfortable—this will be lateral recumbency most of the time. She must not be restricted to lying supine because of resultant aortocaval compression and its potential to lower uterine perfusion (Chap. 4, p. 60). Bloom and colleagues (1998) conducted a randomized trial of walking during labor in more than 1000 women with low-risk pregnancies. They found that walking neither enhanced nor impaired active labor and that it was not harmful. Lawrence and associates (2009) reached similar findings in their Cochrane database review.
This is discussed in detail in Chapter 25. In general, pain relief should depend on the needs and desires of the woman. The American College of Obstetricians and Gynecologists (2009) has specified optimal goals for anesthesia care in obstetrics.
If the membranes are intact, there is a great temptation, even during normal labor, to perform amniotomy. The presumed benefits are more rapid labor, earlier detection of meconium-stained amnionic fluid, and the opportunity to apply an electrode to the fetus or insert a pressure catheter into the uterine cavity for monitoring. The advantages and disadvantages of amniotomy are discussed in Chapter 26 (p. 531). Importantly, the fetal head must be well applied to the cervix and not be dislodged from the pelvis during the procedure to avert umbilical cord prolapse.
Urinary Bladder Function
Distention of the bladder should be avoided because it can hinder descent of the fetal presenting part and lead to subsequent bladder hypotonia and infection. During each abdominal examination, the suprapubic region should be inspected and palpated to detect distention. If the bladder is readily seen or palpated above the symphysis, the woman should be encouraged to void. At times, those who may be unable to void on a bedpan may be able to ambulate with assistance to a toilet and successfully void. If the bladder is distended and voiding is not possible, catheterization is indicated. Carley and coworkers (2002) found that 51 of 11,332 vaginal deliveries (1 in 200) were complicated by urinary retention. Most women resumed normal voiding before discharge from the hospital. Musselwhite and associates (2007) reported retention in 4.7 percent of women who had labor epidural analgesia. Risk factors for retention were primiparity, oxytocin-induced or -augmented labor, perineal lacerations, operative vaginal delivery, catheterization during labor, and labor duration > 10 hours.
Management of the Second Stage of Labor
With full cervical dilatation, which signifies the onset of the second stage, a woman typically begins to bear down. With descent of the presenting part, she develops the urge to defecate. Uterine contractions and the accompanying expulsive forces may now last 1 minutes and recur at an interval no longer than 1½ minute. As discussed on page 447, the median duration of the second stage is 50 minutes in nulliparas and 20 minutes in multiparas, although the interval can be highly variable. Monitoring of the fetal heart rate is discussed on page 450, and interpretation of second-stage electronic fetal heart rate patterns is discussed in Chapter 24 (p. 487).
In most cases, bearing down is reflexive and spontaneous during second-stage labor. Occasionally, a woman may not employ her expulsive forces to good advantage and coaching is desirable. Her legs should be half-flexed so that she can push with them against the mattress. When the next uterine contraction begins, she is instructed to exert downward pressure as though she were straining at stool. A woman is not encouraged to push beyond the completion of each contraction. Instead, she and her fetus should be allowed to rest and recover. During this period of actively bearing down, the fetal heart rate auscultated immediately after the contraction is likely to be slow but should recover to normal range before the next expulsive effort.
Several positions during the second stage have been recommended to augment pushing efforts. Eason and colleagues (2000) performed an extensive review of various positions and their effect on the incidence of perineal trauma. They found that the supported upright position had no advantages over the recumbent one. Upright positions include sitting, kneeling, squatting, or resting with the back at a 30-degree elevation. Conversely, in their systematic review, Berghella and coworkers (2008) reported good-quality data that supported the upright position. Fetal and obstetrical outcomes appear to be unaffected whether pushing is coached or uncoached during second-stage labor (Bloom, 2006; Tuuli, 2012). The maternal effects of coached pushing were reported by Schaffer and colleagues (2005), who performed urodynamic testing in primigravidas 3 months following delivery. Women coached to push during second-stage labor had decreased bladder capacity and decreased first urge to void compared with women encouraged to push or rest as desired. The long-term effects of this practice are yet to be defined.
As the head descends through the pelvis, the perineum begins to bulge and the overlying skin becomes stretched. Now the scalp of the fetus may be visible through the vulvar opening. At this time, the woman and her fetus are prepared for delivery, which is described in Chapter 27 (p. 537).
LABOR MANAGEMENT PROTOCOLS
An orderly and systematic approach to labor management results in reproducible maternal and perinatal outcomes. This was proven by Althabe and coworkers (2008), who randomized implementation of evidence-based care in 19 hospitals in Argentina and Uruguay. Several labor management protocols are subsequently presented. These include those from the National Maternity Hospital in Dublin, the World Health Organization, and from Parkland Hospital.
Active Management of Labor
More than 30 years ago, O’Driscoll and associates (1984) pioneered the concept that a disciplined, standardized labor management protocol reduced the number of cesarean deliveries for dystocia. Their overall cesarean delivery rate was 5 percent in the 1970s and 1980s with such management. The approach is now referred to as active management of labor. Two of its components—amniotomy and oxytocin—have been widely used, especially in English-speaking countries outside the United States. With this protocol, labor is diagnosed when painful contractions are accompanied by complete cervical effacement, bloody “show,” or ruptured membranes. Women with such findings are committed to delivery within 12 hours. Pelvic examination is performed each hour for the next 3 hours, and thereafter at 2-hour intervals. When dilatation has not increased by at least 1 cm/hr, amniotomy is performed. Progress is again assessed at 2 hours and high-dose oxytocin infusion, described in Chapter 26 (p. 530), is started unless dilatation of at least 1 cm/hr is documented. Women are constantly attended by midwives. If membranes rupture before admission, oxytocin is begun for no progress at the 1-hour mark.
López-Zeno and colleagues (1992) prospectively compared such active management with their “traditional” approach to labor management at Northwestern Memorial Hospital in Chicago. They randomly assigned 705 nulliparas with uncomplicated pregnancies in spontaneous labor at term. The cesarean delivery rate was significantly lower with active versus traditional management—10.5 versus 14.1 percent, respectively. Subsequent studies did not show this. Wei and associates (2009) in a Cochrane database review found a modest reduction in cesarean delivery rates when active management of labor was compared with standard care. Frigoletto and coworkers (1995) reported another randomized trial with 1934 nulliparous women at Brigham and Women’s Hospital in Boston. Although they found that such management somewhat shortened labor, it did not affect the cesarean delivery rate. These observations have since been reported by many others (Brown, 2008).
World Health Organization Partograph
A partograph was designed by the World Health Organization (WHO) for use in developing countries (Dujardin, 1992). According to Orji (2008), the partograph is similar for nulliparas and multiparas. Labor is divided into a latent phase, which should last no longer than 8 hours, and an active phase. The active phase starts at 3 cm dilatation, and progress should be no slower than 1 cm/hr. A 4-hour wait is recommended before intervention when the active phase is slow. Labor is graphed, and analysis includes use of alert and action lines. Lavender and colleagues (2006) randomized 3000 nulliparous women to labor interventions at 2 hours versus 4 hours as recommended by WHO. Their cesarean delivery rate was unaffected, and they concluded that interventions such as amniotomy and oxytocin were needlessly increased using the 2-hour time interval. After their Cochrane Database review, Lavender and associates (2008) do not recommend use of the partograph for standard labor management.
Parkland Hospital Labor Management Protocol
Women are admitted if active labor—defined as cervical dilatation of 3 to 4 cm or more in the presence of uterine contractions—is diagnosed or if ruptured membranes are confirmed. Management guidelines summarized in Figure 22-25 stipulate that a pelvic examination be performed approximately every 2 hours. Ineffective labor is suspected when the cervix does not dilate within approximately 2 hours of admission. Amniotomy is then performed, and labor progress determined at the next 2-hour evaluation. In women whose labors do not progress, an intrauterine pressure catheter is placed to assess uterine function. Hypotonic contractions and no cervical dilatation after an additional 2 to 3 hours result in stimulation of labor using the high-dose oxytocin regimen described in Chapter 26 (p. 530). The goal is uterine activity of 200 to 250 Montevideo units for 2 to 4 hours before dystocia can be diagnosed.
FIGURE 22-25 Schematic of labor management protocol in use at Parkland Hospital. The total admission-to-delivery times are shorter than the potential sum of the intervention intervals because not every woman requires every intervention.
Dilatation rates of 1 to 2 cm/hr are accepted as evidence of progress after satisfactory uterine activity has been established with oxytocin. This can require up to 8 hours or more before cesarean delivery is performed for dystocia. The cumulative time required to effect this stepwise management approach permits many women to establish effective labor. This management protocol has been evaluated in more than 20,000 women with uncomplicated pregnancies. Importantly, these labor interventions and the relatively infrequent use of cesarean delivery did not jeopardize the fetus-newborn.
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