Infants delivered via cesarean section may have about twice the risk of becoming obese as infants delivered vaginally, according to a new study published in the journal Archives of Disease in Childhood.
Researchers recruited more than 1,250 pregnant women from the Boston area and followed their children until the age of 3.
They found that at 3 years old, 15.7 percent of children delivered by C-section were already obese, while only 7.5 percent of children delivered vaginally were obese.
The mother's body mass index and the baby's weight at birth did not play a big role in predisposing children to obesity, the researchers explained. Previous research, however, has linked maternal obesity to obesity in their children.
Dr. Susanna Huh, lead author and an assistant professor of medicine at Harvard Medical School, said the findings still need to be confirmed in later studies, but they suggest that women considering having a C-section that isn't medically necessary should know that their children may be at higher risk for obesity.
"Almost one in three children are delivered by C-section in the U.S., and if cesarean delivery is a risk factor for obesity, this would be an important reason to avoid them if they aren 't necessary," Huh said.
But not all mothers who had elective cesareans would heed that advice.
Morgan Roberts of Wilton, Conn. opted for C-sections when she had both of her children, now 4 and 2. She went that route because the first time, she said, she was experiencing joint pain from Lyme disease. For her second child's birth, she wasn't having any medical problems, but just chose to have a C-section.
"They are literally the opposite end of the spectrum from obese," she told ABC News in an email. "As a matter of fact, I have to increase their calories as much as I can because they are superactive and actually below weight."
Roberts said even if she knew about this relationship between obesity and C-section deliveries, she would not have changed her mind. She believes that diet and exercise play a much bigger role in childhood obesity.
"Had all this research come out before I chose to have my C-section I would not have been swayed at all," she said. "I am a very active adult, (as well as my husband), and we strongly value eating well and engaging our children in a variety of activities."
The mechanism behind the relationship between C-sections and obesity is unknown, but Huh and her co-authors speculated there could be a few possible explanations.
"One possibility is that different modes of delivery may affect the bacterial communities established in the body at birth. This could affect obesity by affecting the absorption of nutrients from the diet, or the bacteria in the gut might interact with host cells in ways that promote obesity," she said.
"Another possible explanation is that hormones and protein signals released during labor may have an effect on the development of obesity," she added.
But Dr. Ann Budzak-Garza, a pediatrician with Gundersen Health System in La Crosse, Wis., said based on her experience as a physician, the findings are inexplicable.
"Our C-section rate at Gundersen is only about 20 percent, which is a lot lower than what's reported in the study," she said. "But the incidence of childhood obesity in La Crosse County is actually higher than in other parts of the country. One in three children is overweight or obese."
But she did say that if there is such a relationship, breastfeeding may play a role.
"It's well known that breastfeeding decreases the chances of obesity in children. A C-section makes breast feeding more challenging, and surgery delays when the milk comes in usually by at least a day. It's also a major abdominal surgery, which is painful."
The authors didn't find that feeding played a role, but the data could be hiding something that's difficult to find.
Other than some small studies, there hasn't been much research that explored the association between obesity and type of delivery, Huh said.
Holzman said while he wasn't very familiar with the link between obesity and C-section delivery, the study is important because it reinforces the message that unnecessary cesareans can be dangerous to mothers and babies.
"C-section babies are known to have a bit more breathing problems around the time of birth and a bit higher incidence of ending up in the neonatal intensive care unit. There are also potential risks related to feeding problems, and this study suggests there might also be another effect," he said. "It's worth thinking about whether there are other impacts of C-sections."