BOSTON (Reuters) - More than half of all Cesarean deliveries are done by choice and more than a third are done too early, putting the babies at risk of breathing and other difficulties, U.S. researchers reported Wednesday.
The study of 13,258 births found that the risk of complications doubled if an elective C-section was performed at 37 weeks, when the baby is classified as full term, instead of at 39 weeks when the American College of Obstetricians and Gynecologists (ACOG) regards the operation as safe.
At 38 weeks, the risk of complications was 50 percent higher, the researchers reported in the New England Journal of Medicine.
"Even those deliveries done about three days prior to 39 weeks still have an increase in these adverse outcomes," said Dr. Alan Tita of the University of Alabama at Birmingham, who led the study.
Despite the ACOG guidelines, 36 percent of the babies were delivered early, and the research may have underestimated the risk of complications.
One reason: the study was done at 19 academic hospitals where doctors are usually more attuned to national guidelines. "The assumption is it may be higher if we looked at private physicians in the community," Tita said in a telephone interview.
Another reason is that the researchers had no way of knowing whether a C-section was done after doctors had performed an amniocentisis to confirm that the fetus' lungs had matured. If those cases had been excluded, the risk of early delivery would have been even higher, he predicted.
Why are so many infants being delivered early?
"There is usually this sense that 37 weeks is full term. That's our standard practice," said Tita.
"So women, I believe, when they attain this gestational age, are tired of the pregnancy, they're excited to see the newborn and they start asking to be delivered. So I think part of it is the pressure from the patients who want to be delivered and physicians who want to accommodate their patients."
In a commentary, Dr. Michael Greene of Massachusetts General Hospital said the profile of women who delivered early suggests that they were more likely to be eager to have their own doctor do the delivery.
"To accommodate busy schedules and to minimize the chance that a patient will begin labor and require a nonelective procedure when her doctor might not be available, procedures are frequently scheduled just before 39 weeks of gestation," he said.
The study suggests doctors should not wait too long either. The complication rate rose after 41 weeks, "leaving a relatively narrow two-week window of minimal risk in which elective repeat Cesarean deliveries could optimally be performed," said Greene.
Editing by Maggie Fox and David Wiessler