NEW ORLEANS — Babies born vaginally – or those born by cesarean but exposed to their mother’s vaginal microbiota – have less risk of obesity later in life, a new study released Sunday suggests.

The research analyzed data on 1,441 full-term deliveries from the Boston Birth Cohort, a long-term study of women and their children recruited at Boston Medical Center and funded by the National Institutes of Health. The work revealed that, compared to vaginally delivered babies, C-section delivered children had 40 percent greater odds of becoming overweight or obese in childhood. That finding held true even after researchers accounted for age, race, education, pre-pregnancy body mass and even the child’s birth weight.

“We found the protective effect of vaginal delivery compared to C-section delivery was, if anything, stronger for babies of mothers who were obese or overweight,” said Noel T. Mueller, an assistant epidemiology professor at Johns Hopkins University, and the study’s lead author. Other studies have shown overweight mothers have higher risk of having overweight children, and Mueller’s work suggests vaginal delivery could reduce that intergenerational association.

The study was presented during the American Heart Association’s Scientific Sessions 2016 conference in New Orleans.

At birth, a baby comes into contact with a host of beneficial bacteria in its mother’s vaginal canal, which begins to help form its microbiome, Mueller said. That is the beginning of a kind of ecosystem of beneficial gut bacteria that can play a key role in health, disease and digestion. For C-section babies, that first contact with bacteria is typically from mother’s skin, the physician’s skin or the delivery room.

“Some C-sections, on average about 15 percent in a given population, are medically necessary” to save mother or child, he said. “C-section is a life-saving technique, the importance of which can’t be underemphasized. But sometimes medically unnecessary C-sections may be increasing the risk of obesity and other diseases.”

About one in three births in the United States are done through Cesarean section, according to the Center for Disease Control and Prevention.

Mueller, whose work focuses on obesity and related metabolic outcomes, said more study is needed to look into whether swabbing babies with their mother’s natural bacteria, a process called “vaginal seeding,” can help give extra protection to C-section delivered babies.

Early this year, a paper published in Nature Medicine, showed researchers used the seeding  process to restore vaginal microbes to C-section babies minutes after birth. That study was led by Maria Gloria Dominguez-Bello an associate professor at New York University’s School of Medicine.

Mueller has worked with Dominguez-Bello in the past and plans to team up again.

“What we would like to do is conduct a larger trial,” he said. “the next steps are to hone in on what might be that protective mechanism. … There are still a lot of question marks to be answered.”

For about 15 years, advancing technology has helped scientists sequence bacterial DNA and investigate how microorganisms in the digestive tract colonize, function and potentially help human health.

“We have found there are more beneficial bacteria helping in human health than there are pathogenic (harmful, infectious) bacteria,” he said. “People are starting to appreciate bacteria in ways they haven’t previously.”