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Women who are managing low-risk pregnancies are advised to follow the “39-week rule” – waiting until they are 39 weeks to deliver. This rule is intended to eliminate elective inductions and cesarean deliveries at 37 and 38 weeks, when outcomes for the newborns are believed to be worse than those born at full term.

But new research by a Baylor College of Medicine epidemiologist suggests that babies delivered after elective induction at 37 to 38 weeks may not have an increased risk of adverse neonatal outcomes, compared to those infants who are expectantly managed (i.e., medical observation or “watchful waiting”) and delivered at 39 to 40 weeks. The findings appear in the current issue of Obstetrics and Gynecology.

“Our findings caution against a general avoidance of all elective early-term inductions and call for continued research, based on better data, in what is still a relatively new arena,” said Dr. Jason Salemi, assistant professor of family and community medicine at Baylor and lead author of the study.

The national initiative to eliminate all elective deliveries before 39 weeks began to gain momentum around 2008, Salemi said, and was supported by professional organizations and adopted by healthcare institutions.

“Until then, I had never observed a campaign so enthusiastically embraced and that resulted in such widespread implementation of practice improvement efforts,” Salemi said.

But he saw limitations in many studies used to justify the 39-week rule. Most notably, he recognized what he believed to be an inappropriate choice of comparison group for elective early-term deliveries.

“A number of studies reporting worse outcomes for elective early-term deliveries compared them with later term spontaneous deliveries, a low-risk group. However, the clinical decision that must be made is not between elective early-term delivery and later spontaneous delivery, but between elective early-term delivery and expectant management, in which the outcome remains unknown,” Salemi said.

Salemi and his colleagues conducted a retrospective cohort study that used data on more than 675,000 infants from a statewide database. All live births were classified on the basis of the timing and reason for delivery. The research study compared elective inductions and cesarean deliveries at 37 to 38 weeks to expectantly managed pregnancies delivered at 39 to 40 weeks.

“We focused on serious conditions in early life. Our outcomes included neonatal respiratory morbidity, sepsis, feeding difficulties, admission to the neonatal intensive care unit and infant mortality,” Salemi said.

Salemi cautions that the research findings do not lend support for elective deliveries before 39 weeks and, in fact, provide evidence that supports the avoidance of elective early-term cesarean deliveries. The study found that infants delivered after cesarean delivery at 37 to 38 weeks had a 13 to 66 percent increase in the odds of damaging outcomes.

However, infants delivered after elective early-term induction experienced odds of adverse neonatal outcomes that were largely the same as infants who were expectantly managed and delivered at 39 to 40 weeks. Through the research findings, Salemi hopes to increase awareness on the many issues that surround the timing and reasons for delivery.

“Each pregnancy is unique,” He said. “I cannot overstate the importance of open and ongoing communication between pregnant women and their healthcare providers so that the potential risks and benefits of any pregnancy-related decision are understood fully.”

Other authors that contributed to this research study and article are Dr. Elizabeth Pathak, during her time as an associate professor of epidemiology at the University of South Florida Morsani College of Medicine, and Dr. Hamisu Salihu, professor and vice chair for research in family and community medicine at Baylor.

This research was funded by the Agency for Healthcare Research and Quality (grant number R01HS019997).