FRIDAY, Feb. 10 (HealthDay News) -- A new childbirth study says 39 weeks' gestation is the best time for elective Cesarean delivery for women who have previously delivered via C-section.

The research was slated for presentation Friday at a meeting of the Society for Maternal-Fetal Medicine in Dallas.

"Prior studies have compared the perinatal risks of elective delivery at 37 to 41 weeks' gestation, but didn't evaluate the hazard of delivery versus not delivering at a specific time point," Dr. Giuseppe Chiossi, who conducted the study for the U.S. National Institute of Child Health and Human Development, said in a society news release.

"We wanted to compare the risks of elective repeat Cesarean at each gestational age starting at 37 weeks with the cumulative maternal and neonatal risks of not delivering at that particular gestational age," Chiossi said.

The researchers found that elective repeat Cesarean deliveries at a later gestational age were associated with much lower rates of poor health results for infants compared to deliveries at 37 and 38 weeks.

They also found that poor infant results were much more frequent in pregnancies that continued beyond 39 weeks compared to those in which the baby was delivered through elective surgery at 39 weeks.

Mothers' health results tended to be better with continued pregnancy rather than elective Cesarean at 37 or 38 weeks, but the difference was significant only at 37 weeks. Mothers' results were much worse for later deliveries compared to elective Cesarean at 39 weeks.

Research presented at medical meetings should be considered preliminary until published in a peer-reviewed medical journal.

More information

The American Academy of Pediatrics has more about Cesarean section.