Superior natural cycle pregnancy outcomes following first frozen–thawed embryo transfer in overweight and obese women: retrospective cohort study

Research questionDo endometrial preparation protocols affect pregnancy outcomes in overweight/obese women with a normal ovulatory cycle undergoing their first frozen-thawed embryo transfer (FET)?DesignThis retrospective cohort study analyzed 3713 overweight/obese women with a normal ovulatory cycle who underwent their first FET between January 2018 and October 2023. Patients were divided into two groups based on the endometrial preparation protocol: natural cycle (NC) and artificial cycle (AC). Propensity score matching (PSM) was employed to match baseline characteristics between the two groups at a 1:1 ratio.ResultsAfter PSM, 1238 patients were included in NC and AC groups. The NC group had significantly higher rates of biochemical pregnancy [53.6% (664/1238)], clinical pregnancy [44.7% (554/1238)], ongoing pregnancy [36.2% (445/1229)], and live birth rates [34.7% (427/1229)] compared with the AC group [49.5% (613/1238), P=0.04; 40.3% (499/1238), P=0.025; 32.0% (394/1230), P=0.029; 30.6% (376/1230), P=0.027]. No significant differences were identified between the NC and AC groups in the incidence of perinatal complications or neonatal outcomes (all P>0.05). After adjusting for confounders using multivariate logistic regression analysis, NC remained an independent protective factor for live birth in FET cycles (odds ratio (OR)=1.298, 95% confidence interval (CI): 1.004-1.678, P=0.046). Further subgroup analysis of overweight or obese women revealed consistent findings among overweight women, whereas no statistically significant association between endometrial preparation regimen and the live birth rate in obese women.ConclusionFor overweight/obese women with a normal ovulatory cycle, NC-FET results in better pregnancy outcomes compared with AC-FET without increasing the incidence of obstetric complications.