Children born by cesarean delivery appear to have higher odds of developing obesity than their peers who experienced vaginal births, a U.S. study suggests.
Women who had surgical deliveries known as C-sections were also more likely to be overweight, or to develop complications like diabetes and high blood pressure during pregnancy, than women who had vaginal births, the study found.
After these maternal factors were taken into account, delivery by C-section was still linked to a 15 percent increase in the risk of obesity by the time babies reached adolescence and early adulthood.
"I was expecting that after controlling for these factors the association between cesarean birth and childhood obesity would completely disappear," said senior study author Dr. Jorge Chavarro, a public health and nutrition researcher at Brigham and Women's Hospital and Harvard Medical School in Boston.
"That was not the case," Chavarro added by email.
Even within families, children born by C-section were 64 percent more likely to be obese than their siblings born by vaginal delivery, researchers report in JAMA Pediatrics.
Children born by vaginal birth to women with a previous cesarean delivery were 31 percent less likely to be obese than kids born to women with repeated cesarean deliveries, the study also found.
While cesarean deliveries are often necessary to save lives and prevent injuries, they may also leave babies vulnerable to chronic health problems such as asthma, diabetes and obesity, some previous research suggests.
To explore the connection between C-section deliveries and obesity in particular, Chavarro and colleagues examined data on 22,068 children born to 15,271 women, including 4,921 born by cesarean delivery.
From 1996, when the kids were between 9 and 14 years old, through 2012, when most participants were in their mid-to-late 20s, the researchers tracked their weight and height.
One limitation of the study is that researchers lacked data on why women had C-sections or other aspects of labor and delivery, the authors note.
The study also didn't show why C-sections might make obesity more likely, though the authors say it's possible babies delivered this way may not be exposed to good bacteria in the birth canal that help build the immune system and ward off obesity and other diseases.
Still, the findings offer the strongest epidemiologic evidence to date that C-sections may cause obesity, said Dr. Jan Blustein, a health policy researcher at New York University who wasn't involved in the study.
"When cesarean is indicated, it can save lives," Blustein said by email. "But experts agree that too many cesareans are performed without clear indication."
Ideally, no more than 15 percent of deliveries should be C-sections, according to the World Health Organization. That's the approximate proportion of births that require surgical intervention to protect the mother or infant in situations such as prolonged labor, fetal distress or a breech baby.
In the U.S. and many other developed nations, however, C-section rates are more than double what WHO recommends.
While the study doesn't show why C-sections may be associated with obesity, women should still aim to maintain a healthy weight before getting pregnant and keep weight gain to a healthy range during pregnancy, said Dr. Amos Grunebaum, director of obstetrics at New York-Presbyterian Hospital Weill Cornell Medical Center.
"Because of increased risks, mostly to the mother, cesareans should be done only for proper indications," Grunebaum, who wasn't involved in the study, said by email.
Still, these deliveries have their place, he emphasized.
"The speculative future risk of obesity in the offspring should never be a good enough reason to not do a cesarean, especially when it's done to save the baby's or mother's life," Grunebaum said.