The aim of this study was to explore the impact of female body mass index (BMI) on cumulative live birth rates (CLBR) in patients treated with in vitro fertilization (IVF) and embryo transfer. A total of 2377 patients who visited the Reproductive Medical Center, Luoyang Maternal and Child Health Hospital from January 2015 to December 2021. The patients underwent the first IVF cycles. According to female BMI, patients were divided into 3 groups, group A: BMI ≤ 18.5 kg/m2 (underweight), group B: BMI: 18.5 to 24.0 kg/m2 (normal), group C: BMI ≥ 24.0 kg/m2 (overweight/obesity). Patient basic parameters and clinical outcomes were compared among these 3 groups. Multivariate logistic regression analysis was used to explore the impact of BMI on CLBR. In all treatment cycles, patients' basic parameters were significantly different among 3 BMI groups. Age of underweight patient was younger than patients in the other 2 groups (28.45 ± 5.32 vs 29.89 ± 5.00 vs 30.74 ± 5.40; P = .000). In addition, number of oocytes retrieved was also significantly higher in group A (11.25 ± 5.97 vs 11.07 ± 5.49 vs 10.52 ± 5.02; P = .000). CLBR in these 3 groups were 66.40%, 65.98%, and 59.14%, respectively. In logistic analysis, overweight/obesity was associated with CLBR in young patients (aOR = 0.822, 95% CI: 0.817-0.957, P = .000). However, in the cycles of older patients, the effect of overweight/obesity on the CLBR was not significant (aOR = 0.986, 95% CI: 0.903-1.027, P > .05). Overweight/obesity is a predictor for CLBR in younger patients (<35 years old), but not in advanced age patients undergoing their first IVF/intracytoplasmic sperm injection treatment cycles.