Babies born by cesarean deliveries are no more likely to be obese later in life than babies born vaginally, says a new study.
Despite some past research suggesting a link, Australian researchers found 21-year-olds' weights and waist sizes weren't tied to the way they had been delivered.
"This data does not support the idea that C-section is the reason we have childhood and increasing obesity rates," Dr. Loralei Thornburg said. She is a high-risk pregnancy expert at the University of Rochester Medical Center in New York, but wasn't involved in the study.
"Although both are on the rise … they are not causally linked," she said.
About a third of all deliveries in the U.S. use cesarean procedures, also known as C-sections, according to the Centers for Disease Control and Prevention. About the same proportion of American adults are obese.
Some studies have found a link between C-sections and weight later in life.
Babies delivered by C-section are not exposed to bacteria in the birth canal like vaginally born babies. One theory is that bacteria may somehow protect children from obesity down the road.
Other studies looking at C-sections and obesity, however, haven't found a connection.
Studies that tied C-sections to obesity may not have examined factors that could explain the association, researchers led by Abdullah Mamun from the University of Queensland write in Obstetrics and Gynecology.
Those studies, for example, may not have looked at the mother's weight and health conditions that could increase the likelihood of C-sections and obesity, or whether children were breastfed.
For the new report, the researchers studied 2,625 people who were born between 1981 and 1983 at a hospital in Brisbane, Australia.
Data were periodically collected from those participants and their mothers. That included information on the mother's age and weight during pregnancy, whether or not she had high blood pressure and the child's weight at delivery. The participants' heights, weights and waist sizes were also recorded when they were 21 years old.
About 12 percent of the children were born using C-sections. As young adults, close to 22 percent were considered overweight and about 12 percent were obese.
There was no difference in weight or waist circumference between people born vaginally or via C-sections.
The new finding should be reassuring for women, Thornburg told Reuters Health.
"Just because you ended up with a C-section, you're not damning your child to a life of obesity," she said. "There are so many things that come into play with obesity."
"Even if some of those previous studies that found an association are true, it's not a consistent association," she added.
Thornburg said although there are valid reasons to have a C-section, women should generally be encouraged to have vaginal deliveries.
"Everyone should avoid major abdominal surgery if they can help it," she said, adding that C-sections increase the risk of scars, infections and future complications.
In April, the American College of Obstetricians and Gynecologists said vaginal deliveries should be recommended when there is no sign that the mother or baby would benefit from a C-section.
"The C-section rate in this country is far too high," Thornburg said. "We should absolutely be steering women to vaginal deliveries."