In women with PCOS, being overweight or obese makes IVF less successful. The study found that obese patients retrieved fewer eggs and had lower live‑birth rates, especially when using frozen embryos. Weight loss before starting an IVF cycle could improve the chances of having a baby.

Approximately 50% of the women with polycystic ovary syndrome (PCOS) are overweight or obese and obesity can significantly impair reproductive function. This study aimed to investigate the association between body mass index (BMI) and embryonical/clinical outcomes in PCOS patients undergoing ultralong gonadotrophin-releasing hormone agonist (GnRH-a) protocol and to establish evidence-based management strategies for obese women with PCOS. A total of 1704 PCOS patients aged 20-42 years were treated with an ultralong GnRH-a protocol during a single oocyte retrieval cycle, followed by blastocyst transfer between 2016 and 2023. Participants were stratified according to BMI criteria into four groups: underweight (n = 125), normal weight (n = 845), overweight (n = 517) and obese (n = 217). Baseline characteristic and reproductive outcomes were compared across BMI categories. PCOS patients with obesity exhibited a significant reduction in both the number of retrieved oocytes and mature oocytes. In fresh blastocyst transfer cycles, no statistical differences in live birth rates were observed across the four BMI groups (p = 0.246). However, in frozen-thawed blastocyst transfer cycles, the obese group had the lowest live birth rate among all BMI categories. Multivariate logistic regression analysis identified several key predictors of live birth. The number of high-quality blastocysts transferred was a dominant favorable factor (OR = 1.480, 95% CI 1.251-1.751). Conversely, obesity independently predicted a reduced likelihood of live birth (OR = 0.437, 95% CI 0.298-0.641). Further analysis of cumulative live birth outcomes in a complete oocyte retrieval cycle confirmed that obesity remained a negative predictor (OR = 0.438, 95% CI 0.312-0.615), while the number of high-quality blastocysts transferred (OR = 1.269, 95% CI 1.132-1.423) and a shorter duration of infertility (OR = 0.927, 95% CI 0.885-0.972) were associated with improved success rates. PCOS patients with obesity presented poorer embryonical and clinical outcomes. Obesity emerged as a significant independent predictor of nonlive birth in both frozen-thawed blastocyst transfer cycles and complete in vitro fertilization (IVF) cycles. This study underscores the clinical importance of incorporating pre-IVF interventions, particularly weight management strategies, for obese PCOS patients to optimize reproductive outcomes.