〔Abstract〕 Objective To investigate the correlation between different female body mass index (BMI) values and key indicators of in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) treatment cycles, as well as their impact on obstetric outcomes. Methods A retrospective analysis was conducted on data from patients who underwent IVF/ICSI treatment, with 19 834 cycles included after propensity score matching to balance group differences. Based on the Chinese BMI classification standards with extended categories, patients were stratified into five groups: severely underweight (BMI<16), underweight (16.0 ≤BMI<18.5), normal weight (18.5≤BMI<24.0), overweight (24.0 ≤ BMI<28.0), and obese (BMI ≥ 28.0). Baseline characteristics, ovarian stimulation protocols, treatment processes, and assisted reproductive outcomes were compared among the groups. Additionally, 75 delivered patients with complications were followed up to analyze the association between BMI and pregnancy-related complications. Results No statistically significant differences were observed among the five groups in baseline parameters such as age, duration of infertility, or antral follicle count. Regarding ovarian stimulation protocols and processes, a statistically significant difference was found in the number of IVF oocytes retrieved (P<0.001), with the normal-weight group showing a significantly higher number than both the overweight and obese groups. In terms of assisted reproductive outcomes, no significant differences were observed in biochemical pregnancy rates or birth defect rates. However, cumulative live birth rates differed significantly among the groups (P<0.05), which was significantly higher in the overweight group than in the normal-weight group. Among the 75 followed-up patients, 25 were diagnosed with gestational hypertension, and 22 with gestational diabetes mellitus, of whom overweight and obese individuals accounted for 60.00% and 45.40% of the respective complications. Conclusion Female BMI is significantly associated with IVF/ICSI outcomes. Pre-pregnancy body mass evaluation should be emphasized in patients with extremely low body weight. Although the live birth rate of overweight and obese patients was comparable to that of the normal-weight group, weight reduction prior to treatment is strongly recommended to minimize risks of miscarriage, preterm birth, and pregnancy complications.