A new study led by Columbia University scientists suggests two possible causes of childhood obesity: taking antibiotics during pregnancy and getting a Caesarean section.

The research, published online in International Journal of Obesity, found that children who were exposed to antibiotics during the second or third trimester of pregnancy had a higher risk of obesity at age 7. Authors say the study is the first to explore the effect of antibiotics during those time frames, according to a Columbia University Mailman School of Public Health news release. Previous research has shown that antibiotics administered in early life are liked to an increased chance of childhood obesity.

In the new study, elective and non-elective C-sections were also associated with a higher risk of obesity in offspring.

Antibiotics impact microbes in the body and may enter fetal circulation by way of the placenta, researchers noted. The bacteria that naturally live in the colon help maintain health, and any imbalance in these populations can produce illness. Disturbances in the transmission of bacteria from mother to offspring can increase the child’s chances of developing various ailments, including obesity, the researchers said.

Children who were exposed to antibiotics during the mother’s second and third trimester of pregnancy had an 84 percent higher risk of obesity, compared with children who were not exposed.

“Our findings on prenatal antibiotics and risk for offspring obesity are novel, and thus warrant replication in other prospective cohort studies,” study author Noel Mueller, postdoctoral research fellow at Columbia University’s Mailman School of Public Health and Institute of Human Nutrition, said in the news release. “If these findings hold up, they suggest new mechanisms through which childhood growth trajectories are influenced at the earliest stages of development. Our findings should not discourage antibiotic use when they are medically needed, but it is important to recognize that antibiotics are currently overprescribed.”

The study considered 727 healthy, non-smoking pregnant women recruited at a New York clinic between 1998 and 2006. Study authors tracked 436 of those mothers and their offspring until the children turned 7 years old. According to the press release, 16 percent of the monitored mothers used antibiotics during the second or third trimester of their pregnancies.

In a separate part of the study— which did not consider prenatal antibiotic usage— delivery by C-section was associated with a 46 percent higher risk of childhood obesity.  Researchers considered maternal age, ethnicity, birth weight, sex, breastfeeding in the first year, and gestational antibiotics and delivery mode when analyzing the findings.

Study authors say their conclusions are consistent with previous research.

“While earlier studies suggested that childhood outcomes differ by whether the Caesarean section was elective or non-elective, we did not observe such evidence,” study author Andrew Rundle, associate professor of epidemiology at the Mailman School of Public Health, said in the news release.“Thus, our findings provide new evidence in support of the hypothesis that Caesarean section independently contributes to the risk of childhood obesity.”

Similar to antibiotic usage during pregnancy, C-section births may reduce the normal, healthy transmission of bacteria from mother to child that occurs with a vaginal delivery.

“Strategies to reduce medically unnecessary C-sections and to provide the infant with health-promoting bacteria after C-section need to be researched,” Mueller said.

Rundle pointed out that further research is needed on the ecosystem of bacteria in the human body— namely, its mode of delivery, and how antibiotic use and other factors may influence it.

“This research will help us understand how to create an early platform to support the healthy growth and development of children,” Rundle said.