Beyond the Scale: Effects of Maternal Obesity on Embryo Morphokinetics and IVF Outcomes

Background: Does maternal body mass index (BMI) influence embryo morphokinetics in fresh embryo transfer cycles, and how does this relate to clinical outcomes and obstetric complications? Methods: A retrospective cohort study was conducted on 2238 fresh embryo transfer (ET) cycles, categorized into four BMI groups: underweight, normal weight, overweight, and obese. Baseline characteristics, stimulation parameters, hormonal profiles, morphokinetic data, and pregnancy and delivery outcomes were analyzed. Results: Higher BMI was associated with more anovulatory infertility and greater endometrial thickness. Peak estradiol and estradiol-to-oocyte ratios declined progressively with increasing BMI, despite preserved oocyte yield and embryo quality scores. Interestingly, the underweight group exhibited a significantly distinct biphasic morphokinetics developmental pattern compared with the overweight and obese groups. Pregnancy rates, including clinical and live birth, did not differ significantly across BMI groups. However, obese women had markedly higher cesarean section rates (51.9% vs. ~25–28% in other groups) and a non-significant trend toward more gestational diabetes. Other perinatal outcomes, such as preeclampsia and preterm birth, were not significantly different. Conclusions: In fresh IVF cycles, a higher BMI does not impair pregnancy achievement but is linked to altered hormonal response and increased obstetric risk, particularly cesarean delivery. These findings highlight the importance of preconception counseling and targeted obstetric management for women with elevated BMI undergoing fresh ET.