Association between body mass index and in vitro fertilization/intra-cytoplasmic sperm injection outcomes:An analysis of 15,124 normal ovarian responders in China

Background:High body mass index(BMI)results in decreased fecundity,and women with high BMI have reduced rates of clinical pregnancy and live birth in in vitro fertilization/intra-cytoplasmic sperm injection(IVF/ICSI).Meanwhile,ovarian responses show great heterogeneity in patients with a high BMI.This study aimed to analyze the effects of a high BMI on IVF/ICSI outcomes in the Chinese female with normal ovarian response.Methods:We performed a retrospective cohort study comprising 15,124 patients from the medical record system of the Reproductive Center of Peking University Third Hospital,with 3530(23.3%)in the overweight group and 1380(9.1%)in the obese group,who had a normal ovarian response(5-15 oocytes retrieved)and underwent fresh embryo transfer(ET)cycles from January 2017 to December 2018,followed by linked frozen-thawed embryo transfer(FET)cycles from January 2017 to December 2020.Cumulative live birth rate(CLBR)was used as the primary outcome.Furthermore,a generalized additive model was applied to visually illustrate the curvilinear relationship between BMI and the outcomes.We used a decision tree to identify the specific population where high BMI had the greatest effect on IVF/ICSI outcomes.Results:High BMI was associated with poor IVF/ICSI outcomes,both in cumulative cycles and in separate fresh ET or FET cycles.In cumulative cycles,compared with the normal weight group,obesity was correlated with a lower positive pregnancy test rate(adjusted odds ratio[aOR]:0.809,95%confidence interval[CI]:0.682-0.960),lower clinical pregnancy rate(aOR:0.766,95%CI:0.646-0.907),lower live birth rate(aOR:0.706,95%CI:0.595-0.838),higher cesarean section rate(aOR:2.066,95%CI:1.533-2.785),and higher rate of large for gestational age(aOR:2.273,95%CI:1.547-3.341).In the generalized additive model,we found that CLBR declined with increasing BMI,with 24 kg/m^(2)as an inflection point.In the decision tree,BMI only made a difference in the population aged≤34.5 years,with anti-Mullerian hormone>1.395 ng/mL,and the first time for IVF.Conclusions:High BMI was related to poor IVF/ICSI outcomes in women with a normal ovarian response,and CLBR declined with increasing BMI,partly due to suppressed endometrial receptivity.A high BMI had the most negative effect on young women with anticipated positive prognoses.