WASHINGTON, DC — The optimal time of delivery for women with low-risk pregnancy has been a continuing source of controversy, but a debate on the elective induction of labor at 39 weeks here at American Congress of Obstetricians and Gynecologists 2016 Annual Clinical Meeting turned out to be a statement of consensus.

The two presenters agreed that evidence is mounting that waiting beyond 39 weeks is not advisable.

"Continuing the pregnancy beyond 39 weeks is riskier than previously believed for the fetus," said Errol Raymond Norwitz, MD, PhD, chair of the Department of Obstetrics and Gynecology at the Tufts University School of Medicine in Boston. In addition, risks to the mother associated with routine induction "are lower than appreciated," he said.

"I was absolutely opposed" to the elective induction of labor at 39 weeks, said Charles Lockwood, MD, dean of the Morsani College of Medicine at the University of South Florida in Tampa. In fact, he was prepared to debunk the notion.

But after much reading, "it's overwhelmingly evident that elective induction of labor is the logical strategy," he said.

Members of the audience in the crowded ballroom were won over by Drs Norwitz and Lockwood. Before the presentations, 20% said that it would be best to deliver most women at 39 weeks, 17% were unsure, and 63% were against the idea.

After the presentations, 81% of the attendees said they changed or reconsidered their view. In fact, 70% said they agreed that it is best to deliver most women at 39 weeks, 21% were still unsure, but only 9% were against the idea.

Stillbirth a Bigger Danger Than Realized

Even though higher rates of stillbirth after 39 weeks have been reported since the late 1980s, it still seems to be underappreciated, said Dr Norwitz.

He pointed to several studies that showed that stillbirth is a greater risk at 40 weeks of gestation and beyond.

"Antepartum fetal deaths account for more perinatal deaths than do complications of prematurity or SIDS," he said, citing a report that estimated that there were at least 26,000 stillbirths in the United States in 2004 (BMC Pregnancy Childbirth. 2015;15[Suppl 1]:A11).

Those findings have "been recapitulated in multiple datasets," he explained.

And one study he described showed an increasing risk for stillbirth and neonatal mortality with each passing week of gestation (Br J Obstet Gynaecol. 1998;105:169-173).

It is not known why the rate of stillbirth increases, but it could be related to uteroplacental dysfunction. It might also reflect the failure to identify risk factors, such as multiple pregnancy, infertility, low blood pressure, intrauterine growth restriction, and having previously delivered a small-for-gestational-age infant, he said.

No Increase in Cesarean Rates

The major risk associated with a failed induction at 39 weeks is cesarean delivery, but both Dr Lockwood and Dr Norwitz said that there does not appear to be any evidence of an increase, and that perhaps it might even decrease rates, compared with expectant management.

Some studies have indicated that the rate of cesarean delivery increases in multipara with an unfavorable cervical exam, said Dr Norwitz.

However, data comparing rates of cesarean delivery and other outcomes after induction at 39 weeks and after expectant management at 41 weeks are weak to nonexistent, in part because it would take 2 million to 12 million pregnancies to get good answers, Dr Lockwood explained.

So he and his colleagues conducted a comparative-effectiveness analysis. "We evaluated every conceivable outcome that we could think of," he said. The model involved probabilities for 60 outcomes. The team then created a Monte Carlo microsimulation to map out head-to-head effectiveness.

Expectant management was associated with higher rates of cesarean delivery than induction at 39 weeks, and "a clear increase in perinatal mortality," he reported. Maternal death rates were not significantly different in the two groups, but severe complication rates were lower for both the infant and the mother in the induction group, said Dr Lockwood.

The bottom line is that "elective induction at 39 weeks is always a better strategy" than expectant management at 41 weeks, he said.

Both Dr Norwitz and Dr Lockwood said they agree that success with induction requires very accurate dating of gestational age. "If you're off, you could endanger the patient," said Dr Lockwood.

He also cautioned that induction "has to be a real induction of labor — not one that ends at five o'clock."

Dr Norwitz and Dr Lockwood have disclosed no relevant financial relationships.

American Congress of Obstetricians and Gynecologists (ACOG) 2016 Annual Clinical Meeting. Presented May 16, 2016.