The effect of mildly stimulated cycle versus artificial cycle on pregnancy outcomes in overweight/obese women with PCOS prior to frozen embryo transfer: a retrospective cohort study

Background Previous studies have shown that frozen embryo transfer (FET) resulted in increased live birth rates (LBR) and reduced the risk of ovarian hyperstimulation syndrome (OHSS) than did fresh embryo transfer in women with polycystic ovary syndrome (PCOS). In addition, overweight/obese women with PCOS are at increased risk of subfertility and complications of pregnancy, compared with normal-weight women. The ovarian stimulation and artificial hormone regimes are the two more commonly used endometrial preparation protocols in PCOS patients.This retrospective study aims to compare the pregnancy outcomes of mildly stimulated cycles (mSTC) and artificial cycles (AC) prior to FET in overweight/obese women with PCOS. Methods A retrospective analysis was conducted in overweight/obese women with PCOS who underwent their first FET cycles from January 2018 to December 2020. Two endometrial preparation protocols were used: the mildly stimulated cycles (N = 173) and the artificial cycles (N = 507). All pregnancy outcomes were analyzed by Student's t-test, Chi-square (chi(2)) statistics and multivariable logistic regression analyses. Results This study enrolled 680 cases of FET cycles. The mSTC group exhibited significantly higher LBR compared with the AC group (49.7% vs. 41.0%; P = 0.046), while the rate of miscarriage was significantly lower (6.4% vs. 23.0%; P < 0.001). No statistically significant differences were observed in positive pregnancy rate (57.8% vs. 60.0%, P = 0.618), clinical pregnancy rate (54.3% vs. 55.6%, P = 0.769), and ectopic pregnancy rate (2.1% vs. 3.2%, P = 0.860) between two groups. After adjusting for possible confounding factors, multivariate logistic regression analysis also yielded similar results. Conclusions For overweight/obese women with PCOS, mSTC-FET demonstrated a higher LBR and a lower pregnancy loss rate than that in the AC-FET. When considering the most cost-effective treatment with the least adverse effects on patients, the mSTC for FET endometrial preparation may be considered. To corroborate our findings, additional prospective randomized clinical trials with larger sample sizes are required.