Q&A
Typically labor is induced when the benefits of expeditious delivery outweigh those of continuing pregnancy, although elective inductions are on the rise.1,2 Labor induction is not without consequence, however, most notably the increased risk of cesarean delivery. And once the decision is made to induce labor, the best means may not be entirely clear, particularly when there are so many choices available.What would you do?
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We present 3 scenarios and our recommendations for each. In each case, we cite the supporting evidence to date on the critical questions that lead to an appropriate decision.
| CONDITION | 0 | 1 | 2 | 3 |
|---|---|---|---|---|
| Dilation (cm) | Closed | 1–2 | 3–4 | ≥5 |
| Effacement (%) | 0–30 | 40–50 | 60–70 | ≥80 |
| Station | –3 | –2 | –1,0 | +1,+2 |
| Consistency | Firm | Medium | Soft | — |
| Position | Posterior | Midposition | Anterior | — |
| Source: Bishop EH.4 Reprinted by permission | ||||
CASE 1: Primigravida at 42 weeks
G.C. is a 24-year-old gravida 1 para 0 at 42 0/7 weeks’ gestation, according to her last menstrual period and an ultrasound at 18 weeks. She has had twice-weekly fetal testing since 41weeks’ gestation, with adequate amniotic fluid noted and reassuring results. A nonstress test today was reactive, and the amniotic fluid index is 10.2. Her cervix is closed, firm, and 50% effaced. The fetus is at -3 station and vertex. Estimated fetal weight is 3,500 g. What are the options?
Critical questions
Is she postterm?
Yes. Because the perinatal mortality rate for postterm pregnancies (defined as 42 or more weeks3) is twice that of term gestations, there is evidence to support labor induction after 41 completed weeks. Induction would appear to be justified in this woman’s case.
Is her Bishop score less than 5?
Yes. This patient has an “unfavorable” cervix, according to her Bishop score of 1. (A score of less than 5 is considered unfavorable.) The Bishop scoring system is now generally used to predict the likelihood of successful labor induction, although it was originally used to prevent iatrogenic prematurity in women undergoing elective induction of labor. It is based on clinical findings at the cervical examination: degree of cervical dilation, effacement, consistency, and the position and station of the fetal presenting part.4,5
Is she nulliparous?
Yes. Elective induction should be strongly discouraged in nulliparous patients. Among nulliparous women, an unfavorable Bishop score is associated with almost twice the risk of cesarean delivery when labor is induced rather than spontaneous.6 However, if induction is indicated, cervical ripening may help. Cervical ripening prepares the cervix by promoting dilation and effacement,7 using pharmacologic or mechanical means.
Our recommendations
Although G.C. is nulliparous with an unfavorable cervical examination, her gestational age of 42 weeks provides reason to proceed with induction of labor.
Prostaglandins for cervical ripening
These agents dissolve collagen bundles and increase the submucosal water content of the cervix.8
Off-label but evidence-based. Our prostaglandin of choice is misoprostol (Cytotec), a synthetic prostaglandin E1 analog. Although its use for this purpose is off-label,9 an extensive body of literature attests its safety and efficacy for cervical ripening, provided it is properly administered.10 Misoprostol appears to be more effective than prostaglandin E2 at achieving vaginal delivery within 24 hours.11
Misoprostol is also cheaper and requires no special handling, in contrast to prostaglandin E2.9,12
Caveats. Uterine hyperstimulation and meconium-stained amniotic fluid appear to be more common with misoprostol, although these risks can be minimized by using a dose of 25 μg (1/4 of a 100-μg tablet) at an interval of 3 to 6 hours, with oxytocin given no later than 4 hours after the last dose of misoprostol.11
Prostaglandin administration is associated with increased risk of uterine rupture in women with a prior cesarean delivery or other uterine surgery (SEE CASE 2).13-16 Thus misoprostol and other prostaglandins should be avoided in these women.
Administer prostaglandins in or close to the labor and delivery unit, and where uterine activity and fetal heart rate can be continuously monitored.1 The patient should remain supine for 30 minutes.
Mechanical means of cervical ripening
The 16F Foley catheter is placed transcervically into the extra-amniotic space. The balloon is then inflated with 30 mL of saline and pulled back so that it rests against the internal cervical os.
Low cost. This method of cervical ripening is low in cost and carries less risk of hyperstimulation.17 Thus, it is especially beneficial when the patient needs cervical ripening but is contracting too frequently for safe administration of prostaglandins.