Induction at 41 weeks may cut perinatal complications for low-risk pregnancies

In the United States, the current guidelines state that you should consider induction of labor between 41 0/7 and 41 6/7 weeks of gestation and recommend induction between 42 0/7 and 42 6/7 weeks. This study demonstrates that there is a high rate of spontaneous labor among women who are managed with expectant management. Of the women randomized to the expectant management group, only 19% had not gone into labor by 42 weeks and thus, ultimately required induction.

In addition, there is only a 2-day difference in the gestational age of delivery between the induction and expectant management groups. The difference of 2 days does not change the rate of cesarean section or meconium aspiration system. There was a decrease in the rate of the composite neonatal outcome with induction which was mainly related to Apgar less than 7 at 5 minutes. Other significant neonatal outcomes were very rare in the study population (3 vs. 8 neonatal ICU admissions and 0 vs. 2 meconium aspiration).

However, arterial pH, a common marker of adverse neonatal outcomes, was not collected in 70% of the individuals enrolled this study. The rare rate of neonatal complications may reflect the relatively homogenous (about 86% white) and healthy population (about 11% of body mass index greater than or equal to 30).

Further, the lack of difference must be looked at with some caution as the rate of cesarean sections in the study population (11%) is much lower than the cesarean section rate in the United States of 32%. The absolute number of neonates with meconium aspiration system is very low in the study (0.2% for expectant management and none with induction). Previous studies on this subject have demonstrated rates 10-fold higher than in this current study.

In a related editorial, Kenyon et al. are correct in noting that by excluding Apgar scores, the composite adverse neonatal outcome loses its statistical significance (BMJ 2019 Feb 20. doi: 10.1136/bmj.l681). But, the study did not routinely collect arterial pH, which could be an objective measure of neonatal acidemia; thus, Apgar less than 7 at 5 minutes has to remain, as it is associated with neonatal acidemia. Induction should be part of the decision making for patients who are approaching post term. While an induction may alter a birth experience, some individuals opt for this method as evident by 616 individuals who refused enrollment because they desired induction at 41 weeks or the 87 individuals in the expectant management group who desired induction prior to 42 weeks. Thus, this study allows the clinician to provide counseling about the patient’s desires for management of their pregnancy with more information about neonatal outcomes with both expectant management and induction.

This trial, as well as the ARRIVE trial, have studied the effects of induction on a composite neonatal outcome. Both studies note statistical significance with the composite outcome but secondary to rare outcomes, statistical significance is not demonstrated when you look at each individual outcome. The study by Keulen et al. may help guide clinicians in counseling patients about the timing of their induction at late term. In the low-risk patient, these findings may help guide in the timing of induction.

Sarah D. Crimmins, DO, is an assistant professor of obstetrics, gynecology, and reproductive sciences at the University of Maryland, Baltimore, and specializes in maternal-fetal medicine. She was asked to comment on the article by Keulen et al. Dr. Crimmins reported having no conflicts of interest.