In this prospective cohort study, researchers collected data from 33,226 women who participated in the Nurses’ Health Study II and were born between 1946 and 1964. Of the 33,226 women included in the study, 1089 were born by cesarean delivery (3.3%).

Women born by cesarean section were 11% more likely to be obese and had a 46% higher chance of developing type 2 diabetes (T2D) compared with women born by vaginal delivery, according to a study published in JAMA Network Open.

Throughout the study window, participants provided information on weight and diagnosis of T2D every 2 years. The study’s final follow-up period was completed between 2013 and 2015. Pregnancy characteristics and mode of delivery data were collected form participants’ mothers.

To determine relative risk of obesity and development of T2D, researchers used log-binomial and proportional hazards regression, accounting for maternal body mass index (BMI) and other confounding factors. Participants’ average age at baseline was 33.8 years old.

According to authors, “More than 1.2 million cesarean deliveries are performed yearly in the United States, making it the most common inpatient surgical procedure and accounting for nearly one-third of births nationwide.”

However, researches note cesarean deliveries carry an added risk for the mother and child, and many cesarean deliveries in the United States do not have clear indications. This fact raises concern that excess maternal and newborn morbidity and mortality resulting from unnecessary caesarian deliveries may be preventable.

The study found mothers who gave birth via cesarean section had a higher mean pregnancy (BMI), were older, more likely to have preeclampsia, and give birth to a child with low birth weight than women who delivered vaginally.

Results also showed:

Cumulative risk of obesity through end of follow-up was 36.5% (11,722 of 32,137) among women born by vaginal delivery

Cumulative risk of obesity through end of follow-up was 39.9% (434 of 1089) among women born by cesarean delivery

Incidence of T2D per 10,000 person-years was 10.4 among participants born by vaginal delivery

Incidence of T2D per 10,000 person-years was 14.1 among participants born by cesarean delivery

“The associations of cesarean delivery with risks of obesity and type 2 diabetes were of comparable magnitude across each of the low-risk categories for cesarean delivery based on maternal characteristics, separately and when all were simultaneously considered,” researchers said.

It is unclear whether these results can be applicable to men or individuals born today. The underlying mechanisms accounting for the association of cesarean section delivery, obesity, and T2D development are also unclear. However, “growing evidence points to the hygiene theory and changes in the offspring’s gut microbiota,” researchers said.

They note that gut microbiota can modulate host energy harvest from the diet and changes in gut microbiota can be associated with host adiposity and glucose metabolism. “Vaginally delivered neonates are rapidly colonized by microbes from their mother’s birth canal and feces, while neonates delivered by cesarean delivery are colonized by environmental microbes,” researchers said. They continued, “neonates born by cesarean delivery harbor a less diverse gut microbiota, particularly less Bifidobacteria and less Bacteroides spp, which have shown to be protective against obesity.”

Previous studies have found differences in gut microbiota composition by mode of delivery exist in infants and children up to 7 years of age. It is currently unknown whether these differences are sustained long-term into adulthood.

Because this study marks the first time an association with T2D and cesarean delivery has been investigated, researchers urge caution when interpreting results and note future studies ought to take place to replicate the association.

Reference

Chavarro JE, Martín-Calvo N, Yuan C, et al. Association of birth by cesarean delivery with obesity and type 2 diabetes among adult women [published online April 13, 2020]. JAMA Netw Open. doi: 10.1001/jamanetworkopen.2020.2605.