A large randomized trial showed that induction of labor between 39 0/7 weeks and 39 4/7 weeks in nulliparous low-risk women without medical indications for induction was associated with a trend for less perinatal morbidity and mortality, significantly fewer cesarean deliveries, and fewer hypertensive disorders compared to expectant management. The objective of this study was to evaluate the impact of induction of labor between 39 0/7 weeks and 39 4/7 weeks on the incidence of stillbirth in low-risk women in the United States.
We used US vital statistics data from Live Birth and Fetal Death certificates, of births between January 1, 2014, and December 31, 2016. We included singleton deliveries at ≥39 weeks without preexisting maternal risk factors. We excluded women with pregestational diabetes, chronic hypertension, scheduled cesarean delivery, unknown delivery method, or unknown gestational age.
The primary outcome was the stillbirth rate at ≥39 weeks in singleton pregnancies in low-risk women. This represents the number of potentially preventable stillbirths with a policy of induction at 39 weeks. As the ARRIVE trial induced labor in women in the intervention group between 39 0/7 and 39 4/7 weeks, not all stillbirths occurring in the 39th week may be prevented by induction in the 39th week, because some stillbirths could occur in the 39th week in pregnancies that have not yet undergone delivery. Thus, we conservatively estimated that induction of low-risk pregnancies at 39 weeks would prevent about half of the stillbirths in the 39th week. We also calculated the number of inductions needed to prevent 1 stillbirth and the prospective stillbirth rate at ≥39 weeks.
The study was deemed to be exempt from institutional review board approval. Analysis was performed using STATA 15 (StataCorp, College Station, TX).
Results are shown in the Figure . A total of 12,098,773 births, including 155,753 stillbirths, occurred in the United States during our study period. Among 3874 stillbirths at ≥39 weeks, 3584 occurred in low-risk women (stillbirth rate of 0.60 per 1000 births). This represents on average of 1194 stillbirths per year at ≥39 weeks. Assuming conservatively that only half of the stillbirths occurring during the 39th week (n = 1869) in our study period would be prevented by a policy of induction at about the 39th week, the total number of preventable stillbirths during the 3-year study period was 2650 (883 stillbirths per year). The number of inductions at ≥39 weeks in low-risk singleton gestations needed to prevent one stillbirth is 1675.