Effect of body mass index on in vitro fertilization/intracytoplasmic sperm injection–embryo transfer outcomes in women aged ≥37 years: a retrospective study

Objective: Advanced maternal age is associated with reduced ovarian reserve and lower oocyte quality. Whether body mass index (BMI) further influences assisted reproductive technology (ART) outcomes in this population remains unclear. Methods: This retrospective study analyzed 222 patients aged ≥37 years who underwent in vitro fertilization or intracytoplasmic sperm injection with embryo transfer (IVF/ICSI-ET) at the First Affiliated Hospital of Xiamen University between January 2019 and December 2023. Patients were classified by BMI as underweight (<18.5 kg/m²; n = 13), normal (18.5–24.9 kg/m²; n = 154), or overweight (>24.9 kg/m²; n = 55). Controlled ovarian stimulation protocols were individualized according to ovarian reserve. Laboratory and clinical outcomes were compared across groups, and multivariable logistic regression was used to identify factors associated with clinical pregnancy and live birth. Results: BMI, total gonadotropin dose, and use of IVF vs . ICSI differed among groups (all P <0.05). However, oocyte retrieval rate, metaphase II (MII) oocyte rate, cleavage rate, available embryo rate, high-quality embryo rate, biochemical pregnancy rate, clinical pregnancy rate, live birth rate, and miscarriage rate showed no significant differences (all P >0.05). In multivariable analysis, age, infertility duration, and progesterone level on the day of human chorionic gonadotropin (hCG) trigger were independent predictors of clinical pregnancy. Moreover, age and progesterone level on the hCG day were independently associated predictors of live birth (all P <0.05). Conclusions: Among women aged ≥37 years, higher BMI did not significantly affect key laboratory or pregnancy outcomes after IVF/ICSI-ET. Clinical results were mainly influenced by age, infertility duration, and progesterone level on the hCG trigger day.