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Induced labor at 39 weeks may reduce need for cesarean delivery

Healthy nulliparous women who elected to induce labor at 39 weeks gestation had a lower likelihood of cesarean delivery and preeclampsia, and their infants were less likely to require respiratory support, according to research presented at the annual meeting of the Society for Maternal-Fetal Medicine.

Inducing labor without a medical reason in nulliparous women before 41 weeks gestation is not recommended due to concerns of an increased risk for cesarean delivery; however, in recent years, elective induction of labor at 39 weeks has become more common, according to the NIH.

To investigate the benefits and harms of elective induction of labor at 39 weeks compared with expectant management, William Grobman, MD, from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network, conducted a randomized clinical trial of 6,106 low-risk women in their first pregnancy.

Between 39 0/7 weeks and 39 4/7 weeks, 3,062 women were randomly assigned to the labor induction group, and 3,044 women were randomly assigned to the expectant management group. Participants in the expectant management group waited for natural labor to begin and intervention occurred only when necessary.

To determine modified Bishop scores, women underwent cervical examinations from 72 hours before to 24 hours after randomization. Grobman assessed adverse perinatal events, such as morality, severe neonatal morbidity and cesarean delivery.

Results showed that at the time of randomization, an unfavorable modified Bishop score, defined as lower than 5, was present in 63.5% of participants. Delivery was significantly earlier in women in the induction of labor group than those in the expectant management group (39.3 weeks vs. 40 weeks). A composite of adverse perinatal events, including death, respiratory support, infection and birth trauma, was observed in 4.4% of the induction of labor group and 5.4% of the expectant management group (RR = 0.81; 95% CI, 0.64-1.01).

Participants in the induction of labor group experienced a significantly less frequent need for neonatal respiratory support, compared with the expectant management group (3% vs. 4.2%; RR = 7.1; 95% CI, 0.55-0.93). In addition, cesarean delivery (18.6% vs. 22.2%; RR = 0.84; 95% CI 0.76-0.93) and preeclampsia (9.1% vs. 14.1%; RR = 0.64; 95% CI 0.56-0.74) occurred significantly less often in the induction of labor group than the expectant management group.

There were no differences in the perinatal outcome composite or cesarean delivery by race/ethnicity, maternal age greater than 34 years, BMI greater than 30 kg/m², or modified Bishop score less than 5, according to a priori baseline subgroup analysis.

“[Induction of labor] at 39 weeks in low-risk nulliparous women results in a lower frequency of [cesarean delivery] without a statistically significant change in the frequency of a composite of adverse perinatal outcomes,” Grobman concluded. – by Alaina Tedesco

Disclosure: The author reports no relevant financial disclosures.