Obstetrics in Family Medicine: A Practical Guide (Current Clinical Practice) 2nd ed.

19. Induction and Augmentation

Paul Lyons1

(1)

Department of Family Medicine, University of California, Riverside, Riverside, CA, USA

Key Points

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Background

Under most circumstances, the initiation of labor occurs without assistance at the appropriate time. Under some circumstances, however, induction of labor is indicated prior to the onset of labor via natural processes. Table 19.1presents a list of indications for induction. Induction should always be performed for a specific indication and, when possible, under circumstances where cervical status is favorable for delivery.

Table 19.1

Indications for induction

Pre-eclampsia

Chronic hypertension

Diabetes mellitus

Heart disease

Postdates

Rh incompatibility

Fetal abnormalities or demise

Chorioamnionitis

Premature rupture of membranes

Intrauterine growth restriction

Preparation

Prior to induction patients should be carefully assessed for contraindications to induction (see Table 19.2). In addition, cervical status should be assessed. A Bishop cervical score (see Chap. 18) of 8 predicts a success rate for induction approximately equivalent to spontaneous labor.

Table 19.2

Contraindications to induction of labor

Pelvic abnormalities incompatible with vaginal delivery

Placenta previa

Classical cesarean section scar

Full-thickness myomectomy

Hysterotomy

Breech presentation not compatible with vaginal delivery

If the cervical status is not favorable for induction and the need for delivery is not immediate, cervical preparation may be a helpful adjunct in preparing for delivery. Several modalities are available to enhance favorable cervical status, including mechanical and pharmacological options.

Pharmacological Options

Prostaglandin formulations are available including PGE1 (misoprostol) and PGE2 (dinoprostone). Both mimic the prostaglandin activity physiologically present with the onset of spontaneous labor. Misoprostol is available as a pill that can be placed intravaginally (25 μg every 3–6 h). Dinoprostone is available in a gel formulation (0.5 mg/2.5 mg gel). A single dose is placed intracervically and can be repeated in 6–12 h. Contraindications to prostaglandin use include unexplained bleeding per vagina, rupture of membranes, and prior cesarean section. In addition to those general contraindications, dinoprostone is contraindicated in patients with a history of asthma, glaucoma, or myocardial infarction. Side effects include fetal stress and decelerations, hypertonicity, nausea, vomiting, and fever.

Mechanical Options

Two mechanical options are also available for cervical ripening. These are placement of a Foley bulb and hygroscopic dilators (laminaria). A Foley catheter with a 25–50 cc balloon may be inserted above the internal os, inflated, and withdrawn to the internal os. Within 12 h, the cervix can be expected to dilate 2–3 cm. This dilation will be apparent clinically when the Foley bulb falls out of the cervix. The laminaria is placed in the cervix and as the fluid is absorbed the laminaria swells to three to four times its original size within 6–12 h.

Preparation for induction should also include preparation for failure of induction and therefore should only be performed in a setting where access to operative delivery is available.

Induction

Induction is generally performed with oxytocin. Specific protocols vary between institutions and providers should be aware of the specific protocol at their own institution. One potential regimen is 10 units of oxytocin in 1 L fluid. The oxytocin is attached to an infusion pump and is slowly titrated up until adequate contractions are achieved or contraindications to continue induction develop. Complications include hyperstimulation with possible tetanic contractions, abruptio placentae, uterine rupture, precipitous delivery, cord prolapse, and fetal stress. Because of the potential serious nature of these side effects, patients must have vital signs monitored regularly and must have both fetal heart rate and tocodynamometer monitoring during the course of induction. Details of fetal heart rate monitoring are reviewed in Chap. 26.