By RONI CARYN RABIN
More than one third of mothers who chose to undergo a repeat Caesarean section had their babies earlier than medical guidelines recommend, and the earlier the babies were born, the more likely they were to experience a medical complication like respiratory distress, a large study has found.
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Although babies born by Caesarean section after just 37 weeks of pregnancy are considered full-term, the study found they were twice as likely to suffer complications as those born by Caesarean after 39 weeks. Infants born by Caesarean at 38 weeks were 50 percent more likely to have a medical problem than those born at 39 weeks. The complications included respiratory distress, infections, hypoglycemia, being admitted to the neonatal intensive care unit, or being hospitalized for five or more days.
The study, funded by the National Institute of Child Health and Human Development, was published on Thursday in The New England Journal of Medicine.
It is being released amid concern over the rising numbers of preterm births in the United States and the trend of many women and their physicians to schedule Caesarean deliveries, or C-sections, well in advance of the expected due date. Some 30 percent of deliveries were done by Caesarean section in 2006, up from 20.7 percent in 1996. About 40 percent of the 1.3 million Caesareans performed in the United States each year are repeat procedures, though not all are elective.
“There is an understanding that for a baby born at [full] term, the risks are really very low, and many people may just assume that outcomes at 37 weeks may be the same as at 39 weeks,” said Dr. Alan T.N. Tita, the paper’s lead author and an assistant professor of obstetrics and gynecology at the University of Alabama at Birmingham. “We know that is not true.”
He noted that the American College of Obstetricians and Gynecologists recommends elective Caesareans not be performed before the 39th week of pregnancy.
Medical problems also occurred more frequently in the small group of babies delivered by Caesarean at 41 weeks and 42 weeks, the study found.
Researchers reviewed a registry containing detailed information about repeat Caesarean births to mothers who had previously had the procedure at 19 medical centers, all part of the Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network. Of 24,077 Caesarean deliveries performed at term, 13,258 were elective, meaning there was no medical indication for the surgery, the researchers found. Of those, 6.3 percent were performed at 37 weeks and 29.5 percent at 38 weeks.
Overall, 15.3 percent of babies delivered at 37 weeks suffered a complication of some kind, compared with 11 percent of those born at 38 weeks and only 7.3 percent of those born at 40 weeks. One infant, delivered at 39 weeks, died. Doctors noted that even when babies born by Caesarean are delivered at the same week of pregnancy as babies delivered vaginally, they are at higher risk of respiratory difficulties because the process of labor and delivery primes the fetal lungs for breathing air.
Babies delivered by Caesarean section at 37 weeks were 4.2 times more likely than those delivered at 39 weeks to suffer from respiratory distress syndrome, and 3.3 times more likely to be treated for hypoglycemia, 2.9 times more likely to develop an infection or to be suspected of having an infection, and more than twice as likely to be hospitalized for five or more days or to be admitted to the neonatal intensive care unit.
Babies delivered by Caesarean section at 38 weeks were 2.1 times more likely than those delivered at 39 weeks to suffer respiratory distress syndrome, 1.8 times more likely to be hospitalized for five or more days, and 1.7 times more likely to have an infection or be suspected of having an infection. Babies delivered by Caesarean at 38 weeks had a 30 percent increased risk of hypoglycemia and a 50 percent increased risk of being admitted to the neonatal intensive care unit, compared to those delivered at 39 weeks.
“Faced with the likelihood that there is no other problem, I think it’s prudent to wait until 39 weeks to avoid subjecting these babies to adverse outcomes,” Dr. Tita said. He added that he did not think the results would be different for women undergoing a first elective Caesarean section, versus the repeat Caesareans looked at in this study.
Reactions to the study were mixed. Dr. Michael Greene, director of obstetrics at Massachusetts General Hospital, who wrote an editorial that accompanied the article, said the paper quantifies differences in risk that many physicians may not be aware of.
“I would bet if you ask the first 10 obstetricians on the street if they thought it would make a difference to deliver a baby in the second half of the 38th week and the first half of the 39th week, they’d say, ’Nah, it’s not a big difference,’ ” he said. “This study, because of its size and numbers, is able to say, Yeah, it does make a difference.’ ”
At the same time, he said the study only reviewed live births and did not weigh the risk of a potential stillbirth that could occur with a longer pregnancy against the risk of a complication resulting from an earlier Caesarean.
“The apparent simple message from this study is too simplistic,” he said. “There is a tiny, small but real increase in stillbirths late in pregnancy for women who had a prior Caesarean section, as opposed to women with no scar in their uterus” from a previous Caesarean section.
But Dr. Alan Fleischman, medical director of the March of Dimes, said the findings should reinforce the message that “every week counts” in a pregnancy. The women who were more likely to deliver early were white women with private health insurance, and the medical centers were all top-notch hospitals, he noted.
“These are not preterm babies, and these are pregnancies that should have good outcomes,” he said.