Association of overweight and obesity with cumulative live birth rates according to women's age: A cohort study of 26 567 treatment cycles

Objective: To evaluate the effect of age on the association between maternal body mass index (BMI) and cumulative live birth rates (CLBRs) following in vitro fertilization treatment. Method: We retrospectively analyzed the data of 26 567 women undergoing in vitro fertilization/intracytoplasmic sperm injection from 2016 to 2019. We conducted multivariate regression analysis of the association between CLBRs and maternal BMI and age category. Results: A total of 16 626 (62.58%) patients achieved a live birth. Women with obesity had significantly decreased CLBRs compared with women who had normal weight (odds ratio [OR] 0.73 [95% confidence interval (CI), 0.66–0.80]). The significant interaction between age and BMI suggested that the impact of BMI on CLBRs was moderated by women's age (P interaction <0.001). The association between obesity and CLBRs was inverse among women aged <30 years (OR, 0.63 [95% CI, 0.54–0.73]), 30 to 34 years (OR, 0.79 [95% CI, 0.67–0.93]), and 35 to 37 years (OR, 0.71 [95% CI, 0.52–0.98]); however, decreases in CLBRs with obesity were not observed in women aged 38 to 40 years (OR, 1.17 [95% CI, 0.70–1.94]) and ≥ 41 years (OR, 1.25 [95% CI, 0.53–2.96]). Conclusion: Maternal obesity was significantly associated with a lower likelihood of having a live birth, but the risk differed according to women's age. A higher BMI might have a less-pronounced detrimental effect with increasing age.