The study, conducted in part at the University of North Carolina at Chapel Hill School of Medicine, also found that babies delivered at 41 and 42 weeks faced a similarly elevated risk as those delivered before 39 weeks. However, only a very small percentage of newborns in the study were delivered this late.
“What we found is there’s a very tiny window between 39 and 40 weeks where baby outcomes are optimal, and any deviation before or after that 39th week results in increased risk,” said John Thorp, M.D., study co-author and McAllister Distinguished Professor and division director for women’s primary healthcare in the obstetrics and gynecology department at UNC.
Results of the study are published in the Jan. 8, 2009, issue of The New England Journal of Medicine. The lead author is Alan T.N. Tita, M.D., of the University of Alabama at Birmingham. The study was conducted for and funded by the Maternal-Fetal Medicine Units Network of the National Institute of Child Health and Human Development. It took place at 19 academic medical centers across the United States, including UNC Hospitals.
These results are important, Thorp said, because all of the health problems associated with delivery before 39 weeks exact a heavy toll on families, both emotionally and financially. This in turn leads to increased health care costs for society at large.
“Babies born prior to 39 weeks have more feeding difficulties, more breathing difficulties and need more medical support, whether it be artificial ventilation or oxygen support or some form of tube feeding,” he said.
“So it seems like there is a critical window to do these repeat Caesarean sections in the absence of labor,” Thorp said. “You would take somebody’s due date and subtract seven days, and sometime in that seven days would be the optimal time for Caesarean delivery.”
The number of women giving birth by Caesarean section has increased dramatically in the United States in recent years, rising from almost 21 percent of births in 1996 to 31 percent in 2006. At the same time, more C-section deliveries are taking place before the 39th week of pregnancy. Thorp said the earlier deliveries are being driven, at least in part, by the desire for scheduling convenience, both by mothers and physicians.
In the study, researchers analyzed records from more than 28,000 Caesarean sections performed on women who previously had one or more C-sections. Of these, 13,258 were performed electively – that is, without a specific medical indication that a C-section was required. Nearly 36 percent of the elective repeat C-sections were performed prior to 39 weeks while 49 percent were performed at 39 weeks.
Babies delivered at 37 weeks were up to four times more likely than babies delivered at 39 weeks to have breathing problems, require mechanical ventilation, have newborn sepsis (a severe bacterial infection) or hypoglycemia (low blood sugar), to require admission to a neonatal intensive care unit or to spend five or more days in the hospital after birth. Babies delivered at 38 weeks were twice as likely to have one or more of these problems than babies delivered at 39 weeks.
“These early deliveries are associated with a preventable increase in neonatal morbidity and admissions to the neonatal ICU, which carry a high economic cost,” the study concluded. “These findings support recommendations to delay elective delivery until 39 weeks gestation, and should be helpful in counseling.”