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Women born via cesarean section delivery were more likely to develop obesity and type 2 diabetes later in life, according to a retrospective cohort study.

Compared with female infants delivered vaginally, those born by C-section had an 11% greater risk of being obese (95% CI 1.03-1.19), reported Jorge Chavarro, MD, ScD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues.

Female babies delivered via C-section also were more likely to develop type 2 diabetes in adulthood (adjusted hazard ratio 1.46, 95% CI 1.18-1.81), the researchers wrote in .

Chavarro said that these findings on obesity align with previous research. "The most novel aspect of this finding is the fact that the higher rates of obesity among children born by cesarean delivery do not appear to reverse over time, but may result in life-long differences observable throughout adulthood," he told 番茄社区 in an email.

The associations were also comparable across each of eight low-risk groups for C-section that included the absence of gestational hypertension and diabetes, and smoking during pregnancy, the authors noted.

"Most important, the association remained significant in most of the analyses restricted to participants in low-risk categories for cesarean delivery based on maternal characteristics," Chavarro and colleagues wrote. However, they pointed out that when analyzing women in all low-risk categories simultaneously, the association was no longer significant.

Although the mechanisms for development of obesity and type 2 diabetes in babies born by C-section remain unclear, more evidence points to differences in gut microbiota by mode of delivery, the authors stated, adding that neonates delivered vaginally are colonized by microbes from the birth canal and feces, resulting in a more diverse gut microbiota that may affect metabolic health.

Noel Mueller, PhD, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, said that this study is consistent with previous findings on an association of C-section delivery with obesity in offspring.

But the association between C-section and type 2 diabetes makes the current research novel, noted Mueller, who was not involved in the study. "It starts to tell you that C-section may be contributing to metabolic dysregulation beyond just obesity," Mueller told 番茄社区.

Loralei Thornburg, MD, an ob/gyn at the University of Rochester Medical Center in New York, said that the study highlights the importance of looking at pregnancy, and the delivery window, as a critical time for long-term health outcomes.

But Thornburg, who was not involved in the study, cautioned that the lack of data on what indicated the C-section is a major study limitation.

"The things that lead to cesarean delivery also contribute to factors that we know increase adult obesity and adult diabetes," Thornburg told 番茄社区. She added that when the researchers looked at a group with no risk factors for C-section, they did not find a significant association, indicating that pinpointing those elements may be difficult.

More than in the U.S. in 2018 were C-section deliveries, according to the CDC. While C-section deliveries can be a life-saving intervention for both mother and child when medically necessary, the procedure comes with additional risks, Chavarro's group stated.

They obtained data from the Nurses' Health Study II (NHS-II). In 2001, mothers of NHS-II participants completed a questionnaire about the pregnancy and birth of those in the cohort.

The study sample had more than 33,000 NHS-II participants born from 1946 through 1964, and followed up through 2015. Researchers calculated BMI from the height and weight measurements of each participant reported at baseline, and then every 2 years after. Participants also reported physician-diagnosed type 2 diabetes.

Researchers excluded all participants who did not provide information on height and weight, were not born of a singleton pregnancy, and whose mothers did not provide delivery mode information.

Mothers of NHS-II participants retrospectively reported information on race/ethnicity, maternal education level, maternal prepregnancy BMI, gestational diabetes, preeclampsia or gestational hypertension, gestational age, birthweight, and smoking during pregnancy. A validation study showed that this long-term recall of data was accurately reported.

Of the 33,000 participants (mean age 33.8; 97.3% white) in the study, 3.3% were delivered via C-section. The researchers found more than 12,000 cases of obesity and around 2,000 cases of type 2 diabetes among participants.

Participants' mothers that gave birth via C-section had a higher average prepregnancy BMI than those that delivered vaginally. In addition, mothers that gave birth by C-section were older at the time of delivery, and more likely to have preeclampsia, hypertension, preterm birth, and low birthweight.

Cumulative risk of obesity through the end of follow-up among women born via vaginal delivery was 36.5% versus 39.9% among women born via C-section. In addition, researchers found that the incidence of type 2 diabetes per 10,000 person-years was 10.4 among women delivered vaginally versus 14.1 among women born by C-section.

Besides the missing data on indication for C-section, other study limitations included its retrospective nature and reliance on recalled data.

"It is also important to consider the generalizability of the findings to current practice in light of the differences in cesarean delivery rates at the time of the study and today," the authors wrote. "As this is an observational study, further research is needed before causality can be assumed."

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