Women for whom a Caesarean section is a matter of preference might want to consider some new research: Babies born by C-section may be more likely than those delivered vaginally to become obese children.

Research published Wednesday in the BMJ journal Archives of Disease in Childhood looked at records for 1,255 mom/baby pairs; 284 of those babies were delivered by c-section, and 971 were delivered vaginally. 

The researchers analyzed the babies’ BMI and a measure of body fatness called a skin-fold test when the children were 3 years old. Babies delivered by c-section were about twice as likely to be obese at age 3 than those delivered vaginally: 15.7 percent of the babies delivered by c-section were obese compared to 7.5 percent of those delivered vaginally. The kids delivered by c-section were heavier overall and had more body fat, too.

Those findings held up even after accounting for potential confounders such as the mother’s weight, the babies’ size and the length of time for which babies were breastfed. Mothers who delivered by c-section were generally heavier than the others, and their babies were bigger for their gestational age than the vaginally delivered infants. Also, the mothers who had C-sections didn’t breastfeed their babies as long as the other mothers did.

The study notes that C-sections have already been linked to increased risk of asthma among babies.  The authors suggest that C-sections might alter the way babies are exposed to and acquire colonies of key digestive bacteria from their mothers during birth. That might lead to differences in the way they digest food, which could contribute to their becoming obese, the study suggests.

The study cites Centers for Disease Control data showing that nearly a third (32 percent) of births in the U.S. in 2007 were by c-section, up from 20.7 percent in 1996. The authors further note that an estimated 4 percent to 18 percent of C-sections are conducted by “maternal request,” not because they are recommended by the doctor.