Association of Birth by Cesarean Delivery With Obesity and Type 2 Diabetes Among Adult Women.

Importance: Cesarean delivery is associated with an increased risk of childhood obesity in offspring. However, whether this increased risk also includes obesity-associated conditions remains unclear. Objective: To evaluate the association of birth by cesarean delivery with offspring's risks of obesity and type 2 diabetes in adulthood. Design, Setting, and Participants: This prospective cohort study compared the incidence of obesity and type 2 diabetes between birth by cesarean delivery and vaginal delivery among 33 226 women participating in the Nurses' Health Study II who were born between 1946 and 1964, with follow-up through the end of the 2013-2015 follow-up cycle. Participants' mothers provided information on mode of delivery and pregnancy characteristics. Participants provided information every 2 years on weight and diagnosis of type 2 diabetes. Relative risks of obesity and type 2 diabetes were estimated using log-binomial and proportional hazards regression accounting for maternal body mass index and other confounding factors. Statistical analysis was performed from June 2017 to December 2019. Exposure: Birth by cesarean delivery compared with birth by vaginal delivery. Main Outcomes and Measures: Risk of obesity and incidence of type 2 diabetes. Results: At baseline, the participants' mean (SD) age was 33.8 (4.6) years (range, 24.0-44.0 years). A total of 1089 of the 33 226 participants (3.3%) were born by cesarean delivery. After 1 913 978 person-years of follow-up, 12 156 (36.6%) women were obese and 2014 (6.1%) had received a diagnosis of type 2 diabetes. Women born by cesarean delivery were more likely to be classified as obese and to have received a diagnosis of type 2 diabetes during follow-up. The multivariable-adjusted relative risk of obesity among women born by cesarean vs vaginal delivery was 1.11 (95% CI, 1.03-1.19). The multivariable-adjusted hazard ratio for type 2 diabetes among women born by cesarean vs vaginal delivery was 1.46 (95% CI, 1.18-1.81); this association remained significant after additional adjustment for participant's own body mass index (relative risk, 1.34 [95% CI, 1.08-1.67]). These associations persisted when analyses were restricted to women at low risk of cesarean delivery based on maternal characteristics. Conclusions and Relevance: This study suggests that women born by cesarean delivery may have a higher risk than women born by vaginal delivery of being obese and developing type 2 diabetes during adult life.