A clinical trial of induction of labor versus expectant management in postterm pregnancy*,**

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Abstract

OBJECTIVE: Management of the uncomplicated pregnancy prolonged beyond the estimated date of confinement is controversial, particularly when the cervix is unfavorable for induction. The benefit of reducing potential fetal risk with induction of labor must be balanced against the morbidity associated with this procedure. The objective of this study was to compare two strategies for managing postterm pregnancy (i.e., immediate induction and expectant mangement). STUDY DESIGN: Four hundred forty patients with uncomplicated pregnancies at 41 weeks' gestation were randomized to either immediate induction of labor (n = 265) or expectant management (n = 175). Patients with expectant management underwent nonstress testing and amnioic fluid volume assessment twice per week. Patients in the induction group underwent induction within 24 hours of randomization. To evaluate the efficacy of intracervical prostaglandin E2 gel, patients in the induction group were randomized in a 2:1 scheme to receive either 0.5 mg prostaglandin E2 gel or placebo gel intracervically 12 hours before induction of labor with oxytocin. RESULTS: The incidence of adverse perinatal outcome (neonatal seizures, intracranial hemorrhage, the need for mechanical ventilation, or nerve injury) was 1.5% in the induction group and 1% in the expectant management group (p > 0.05). There were no fetal deaths in either group. There were no differences in mean birth weight or the frequency of macrosomia (birth weight ≥ 4000 gm) between the two groups (p > 0.05). Regardless of parity, prostaglandin E2 intracervical gel was not more effective than placebo in ripening the cervix. The cesarean delivery rate was not significantly different in the expectant (18%), prostaglandin E2 gel (23%), or placebo gel (18%) groups. CONCLUSIONS: Adverse perinatal outcome in otherwise uncomplicated pregnancies of ≥41 weeks is very low with either of the management schemes described. Thus from the perspective of perinatal morbidity or mortality either management scheme is acceptable. (AM J OBSTET GYNECOL 1994;170:716-23.)

Section snippets

METHODS

The trial was designed and implemented by the participants of the Maternal-Fetal Medicine Units Network under the direction and sponsorship of the National Institute of Child Health and Human Development. An investigational new drug (IND) exemption for the use of PGE2 gel was obtained from the Food and Drug Administration. Informed consent was obtained from each participating subject.

RESULTS

Between December 1987 and July 1989 we screened 4566 pregnant women who had reached a gestation of ≥41 weeks. Of these, 4126 were ineligible for the study: 2428 (59%) because of uncertain gestational age, 650 (16%) because of a medical or obstetric complication, 549 (13%) because of a Bishop score of ≥7, 72 (2%) because of decreased amniotic fluid volume, and 100 (2%) because of a nonreactive nonstress test. An additional 323 patients (8%), although eligible, refused to participate in the

COMMENT

This study was stopped because the incidence of the primary outcome variable (perinatal mortality or morbidity) was only 1%. Thus a sample size in excess of 5600 would be required to adequately compare the two schemes described. Because adverse perinatal outcome is so uncommon in postterm pregnancy, the cost of such a trial is not justified. Furthermore, the low prevalence of postterm pregnancy in a well-dated population that is eligible for expectant management (i.e., an unripe cervix, a

ADDENDUM

After submission of our manuscript, the Canadian Multicenter Postterm Pregnancy Trial Group also reported the results of a study of postterm pregnancy. Several differences in the current study and the Canadian study limit a direct comparison of most outcome variables. For example, the Canadian investigators used PGE2 intracervical gel repeatedly, if needed. We administered the agent only once. Further, the Canadian investigators defined a cervical dilatation of 3 cm as an entry criterion

References (18)

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*

Reprint requests: Donald McNellis, MD, National Institute of Child Health and Human Development, National Institutes of Health, EPN Building, Room 643, Bethesda, MD 20892.

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