February 23, 2016

If your pregnancy has continued beyond 40 weeks, your OB/GYN may recommend inducing labor – an option many pregnant women refuse because they’re concerned it will stress the unborn baby and increase the likelihood of caesarean section.

A new Israeli study underscores doctors’ recommendations, however, finding that deliveries in the 42nd week or beyond — even among low-risk pregnancies — are associated with increased short-term risks to newborns, including illnesses and infections, which land them twice as frequently in neonatal intensive care units (NICUs).

The study isolates the post-term due date as a single, influential risk factor for the first time. Results were published recently in the Archives of Disease in Childhood: Fetal and Neonatal Edition.

“There are women who refuse induction of labor, even more than two weeks past their due date,” said Dr. Liran Hiersch of Tel Aviv University’s Sackler Medical School and Rabin Medical Center in Petah Tikva.

“Without the relevant data, it is difficult for doctors to convince them otherwise. Maybe now, with this research and further studies in hand, we can convince them that even though their pregnancies had experienced no complications — and they are being monitored, say, every three days — they’re potentially risking infection, illness and other unforeseen complications by refusing medical intervention.”

Along with Dr. Nehama Linder, director of neonatology at Rabin Medical Center, senior OB/GYN Dr. Nir Melamed and neonatologists Elana Fridman, Gil Klinger, Daniel Lubin and Franck Kouadio, Hiersch examined the electronic records of all women who delivered babies at Rabin Medical Center over a five-year period.

The research team focused in on the records 23,524 women with a single fetus and without pregnancy complications who delivered at 39 to 44 weeks of gestation.

Then they compared the neonatal outcomes of three groups: 18,145 full-term infants born at 39 to 40 weeks; 4,632 late-term infants born during the 41st week; and 747 post-term infants born at 42 weeks or later.

“Although previous studies demonstrated an increased risk of complications for newborns born in the post-term period, most of these studies included women with pregnancy-related complications, such as small fetuses, hypertension and diabetes mellitus,” said Hiersch. “The isolated effect of the prolonged pregnancy could not be determined. For this reason, we included in our analysis only women with low-risk pregnancies in order to more clearly determine the effect of gestational age at delivery on neonatal outcome.”

Excluding all cases of stillborn births, the researchers found that infants born past 42 weeks had approximately twice the risk of contracting infections, experiencing respiratory difficulties and being admitted to NICUs than those born at 39 to 40 weeks.

“Our study implies that even in otherwise low-risk pregnancy, it is advisable not to postpone delivery beyond 42 weeks,” said Hiersch. “Therefore, it is reasonable to offer induction of labor to women reaching that time of pregnancy and maybe a little earlier.”

While the study addressed only the complications that occur immediately following birth, the research team is now exploring a larger study that will look into whether post-term deliveries put infants at risk for developmental difficulties later in life.

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Jason Harris

Jason Harris

Executive Director