Researchers at the University of North Carolina at Chapel Hill School of Medicine found that babies delivered by elective Caesarean section before 39 weeks of pregnancy -- to mothers who previously had an elective C-section -- are much more likely to have serious health problems than newborns delivered under the same circumstances at 39 weeks.

The study, published in the New England Journal 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.

"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," study co-author Dr. John Thorp said in a statement.

"So it seems like there is a critical window to do these repeat Caesarean sections in the absence of labor."