While pregnancy is considered full-term at 40 weeks, only some 5 percent of women actually give birth on their predetermined due date. Most OBGYNs recommend more frequent and more vigilant monitoring after 40 weeks and sometimes the artificial induction of labor. But many pregnant women refuse induction due to the risk of stress to the fetus or increased likelihood of requiring a caesarean section.
A new Tel Aviv University study has found that post-term deliveries, 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.
The research was led by Dr. Liran Hiersch of TAU's Sackler Faculty of Medicine and Rabin Medical Center in Israel, together with Prof. Nehama Linder, also of Sackler and director of Rabin Medical Center's Department of Neonatology, and Dr. Nir Melamed of Rabin Medical Center. It was published in December in the Archives of Disease in Childhood, Fetal and Neonatal Edition.
Countering fear with fact
"There are women who refuse induction of labor, even more than two weeks past their due date," said Dr. Hiersch. "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."
Dr. Hiersch and his team examined the electronic records of all women who delivered babies at Rabin Medical Center over a five-year period. They extracted the records of approximately 23,500 women with a single fetus and without pregnancy complications who delivered at 39-44 weeks of gestation. Then they compared the neonatal outcomes of three groups: neonates born at 39-40 weeks; neonates born at 41 weeks; and neonates born at 42 weeks and later, or "post-date pregnancies."
"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 Dr. 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."
The researchers only addressed women who gave birth to live infants, excluding all cases of still-borns, in order to effectively isolate the influence of time of delivery on the infant. They 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 39-40 weeks.
A warning to new mothers
"Our study implies that even in otherwise low-risk pregnancy, it is advisable not to postpone delivery beyond 42 weeks," said Dr. Hiersch. "Therefore, it is reasonable to offer induction of labor to women reaching that time of pregnancy and maybe a little earlier."
In the study, the researchers addressed the complications that occur immediately following birth. They are now exploring a larger study that addresses whether post-term deliveries put infants at risk for developmental difficulties later in life.
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