Williams Manual of Pregnancy Complications, 23 ed.

CHAPTER 35. Preterm Birth: Intact Membranes

There are a number of factors important in the management of the women with possible preterm labor. Foremost is correct identification, along with whether there is accompanying membrane rupture (see Chapter 34).

DIAGNOSIS

Early differentiation between true and false labor is difficult before there is demonstrable cervical effacement and dilatation. Uterine contractions alone can be misleading because of Braxton Hickscontractions. These contractions, described as irregular, nonrhythmical, and either painful or painless, can cause considerable confusion in the diagnosis of preterm labor. Not infrequently, however, women who deliver before term have uterine activity that is attributed to Braxton Hicks contractions, prompting an incorrect diagnosis of false labor.

Because uterine contractions alone may be misleading, the American College of Obstetricians and Gynecologists (Management of preterm labor. Practice Bulletin 78, June 2012) has used the following criteria to document preterm labor between 20 and 37 weeks’ gestation:

1. Regular uterine contractions accompanied with

2. Change in cervical dilation, effacement, or both

3. Initial presentation with regular contractions and cervical dilation of at least 2 cm.

ANTEPARTUM MANAGEMENT

Antepartum management of women with signs and symptoms of preterm labor and intact membranes is much the same as already described for pregnancies with preterm ruptured membranes (see Chapter 34). That is, the cornerstone of treatment is to avoid delivery prior to 34 weeks’ gestation if possible. Drugs intended to suppress uterine contractions are discussed later in this chapter. As in pregnancies with preterm ruptured membranes, antimicrobials, for the purpose of delaying delivery in women with preterm labor, have been studied specifically in women with intact membranes. Results with a variety of antimicrobial agents have been disappointing. It is possible that administration of antimicrobials after preterm labor with intact membranes has begun too late to interfere with propagation of the biochemical cascade that modulates uterine activity.

The treatment regimen that has been used most often for the prevention of delivery is bed rest either in the hospital or at home. However, there is no conclusive evidence that bed rest is helpful in preventing preterm birth. Indeed, enforced bed rest (except for bathroom privileges) for 3 days or more may increase the risk of thromboembolic complications.

Drugs Used to Inhibit Contractions

Many drugs have been used to inhibit preterm labor (tocolysis), but unfortunately, none has been shown to be completely effective. For this reason, pharmacologic tocolysis is not used at Parkland Hospital.

The American College of Obstetricians and Gynecologists (Preterm labor. Technical Bulletin No. 206, June 1995) has made the following statements in regard to tocolytics:

To date, no studies have convincingly demonstrated an improvement in survival or any index of long-term neonatal outcome with the use of tocolytic therapy. On the other hand, the potential damages of tocolytic therapy to the mother and the neonate are well documented. Because of the clear benefit of corticosteroid administration before 34 weeks of gestation, the use of tocolytic agents for short-term prolongation of pregnancy is justified. Otherwise, the question of whether to use tocolytic agents at any gestational age cannot be answered at this time, especially beyond 34 weeks of gestation.

Because of these uncertainties, the American College of Obstetricians and Gynecologists (Management of preterm labor. Practice Bulletin 78, June 2012) has recommended that tocolysis be considered when there are regular uterine contractions plus documented cervical change or appreciable dilatation and effacement and there is a need to administer fetal corticosteroids or magnesium neurorprotection or both. Potential complications of tocolytic therapy are shown in Table 35-1.

TABLE 35-1. Potential Complications of Tocolytic Drugs

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A list of commonly used tocolytics and doses are listed in Table 35-2. Potential complications of tocolytic drugs are listed in Table 35-3.

TABLE 35-2. Commonly Used Tocolytic Drugs

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TABLE 35-3. Magnesium Sulfate for the Prevention of Cerebral Palsya

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Glucocorticoid Therapy

Administration of either betamethasone or dexamethasone to women at risk of preterm delivery is routinely practiced to enhance fetal lung maturation in an effort to minimize respiratory distress syndrome due to prematurity. According to The National Institutes of Health Consensus Development Conference (2000): Statement on Repeat Courses of Antenatal Corticosteroids. Bethesda, MD. August 17–18, 2000. Available at http://consensus.nih.gov/2000/2000AntenatalCorticosteroidsRevisted112html.htm

All women between 24 and 34 weeks of gestation at risk for preterm delivery are candidates for antenatal corticosteroid therapy. Repeat doses of corticosteroids should not be used routinely.

At Parkland Hospital, a single course of betamethasone 12 mg every 24 hours for 2 doses is recommended when preterm labor or rupture of membranes is first diagnosed; follow-up repetitive courses are not given. Many physicians prefer to give a single course of 5 mg of dexamethasone every 12 hours for 4 doses.

Neuroprotection

Available evidence suggests that magnesium sulfate given before anticipated early preterm birth reduces the risk of cerebral palsy in surviving infants. We have elected to use the protocol from the BEAM trial in infants prior to 28 weeks based on the data in Table 35-3 from Rouse and colleagues (2008). A loading dose of 6 g is initiated followed by a maintenance dose of 2 g/h. Treatment is affected for up to 12 hours and resumed when delivery is imminent.

MANAGEMENT OF LABOR AND DELIVERY

In general, the more immature the fetus, the greater the risks from labor and delivery. Abnormalities of fetal heart rate and uterine contractions should be sought during labor, preferably by continuous electronic monitoring. Fetal tachycardia, especially in the presence of ruptured membranes, is suggestive of infection.

Prevention of Neonatal Group B Streptococcal Infections

Group B streptococcal infections are common and dangerous in the preterm neonate. The American College of Obstetricians and Gynecologists (Induction of labor for vaginal birth after cesarean delivery. Committee Opinion No. 271, April 2002) recommends either penicillin G or ampicillin intravenously until delivery for women in labor prior to 37 weeks and whose culture status is unknown or positive for Group B Streptococcus (see Table 35-4).

TABLE 35-4. Regimens for Intrapartum Antimicrobial Prophylaxis for Perinatal Prevention of Group B Streptococcal Disease

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Delivery

In the absence of a relaxed vaginal outlet, an episiotomy for delivery may be advantageous once the fetal head reaches the perineum. Argument persists as to the merits of spontaneous delivery versus forceps delivery to protect the fragile preterm fetal head. It is doubtful whether use of forceps in most instances produces less trauma. Indeed, to compress and pull on the head of a grossly pre-term infant might be more traumatic than natural expulsion. The use of outlet forceps of appropriate size may be of assistance when conduction analgesia is used and voluntary expulsion efforts are obtunded.

A physician and staff proficient in resuscitative techniques and fully oriented to the specific problems of the case should be present at delivery. The importance of the availability of specialized personnel and facilities in the case of preterm infants is underscored by the improved survival of these infants when they are delivered in tertiary care centers.

Cesarean Delivery to Prevent Neonatal Intracranial Hemorrhage

Preterm infants frequently have germinal matrix bleeding that can extend to more serious intraventricular hemorrhage (see Chapter 28). It has been hypothesized in the past that cesarean delivery to obviate trauma from labor and vaginal delivery might prevent these complications. This hypothesis has not been validated by most subsequent studies.


For further reading in Williams Obstetrics, 23rd ed.,

see Chapter 36, “Preterm Birth.”