The frozen-thawed embryo transfer timing determined by serum progesterone level: a retrospective follow-up study

ObjectiveTo compare the reproductive outcomes of frozen-thawed embryo transfer (FET) in nature cycle utilizing monitoring ovulation regimen (MOR) and monitoring progesterone (P) level regimen (MPR).Study designA retrospective analysis of records of 224 women who received FET procedures.Result(s)MPR was used in 60.3% (135/224) of cycles and MOR in 39.7% (89/224) of cycles. The clinical pregnancy rate per transfer was 63.0% in the MPR group and 48.3% in the MOR group (p = 0.030). The implantation rates were 42.6% and 35.1%, respectively (p = 0.001). The ongoing pregnancy rates per transfer (at 12 weeks' gestation) were 54.1% and 41.6%, respectively (p > 0.05). A logistic regression analysis showed that the type of natural cycle regimen was a predictor of clinical pregnancy rate (odds ratio, 1.996; 95% confidence interval, 1.123-3.549; p = 0.019). Other significant variables affecting clinical pregnancy rate was number of top-quality embryos transferred.Conclusion(s)Performing FET using MPR could achieve higher clinical pregnancy rate compared with MOR in a group of patients with the comparable demographic and cycle characteristics profile.