Comparison of pregnancy outcome in patients with thin endometrium undergoing fresh embryos and frozen thawed embryo transfer

Objective To study the differences of pregnancy outcome in patients with thin endometrium underdoing fresh embryo transfer and frozen-thawed embryo transfer (FET). Methods Retrospective analysis was performed in patients with the endometrial thickness ≤ 7 mm on hCG injection day and FET endometrial transformation day who received in vitro fertilization/intracytoplastic sperm injection-embryo transfer (IVF/ICSI-ET) treatment, including 592 cycles of clinical data. According to transplanted embryos whether or not be frozen-thawed, all patients were divided into two groups: fresh embryo transfer group (173 cases), FET group (419 cases). The rates of embryo implantation, clinical pregnancy rate, spontaneous abortion rate, multiple birth rate and ectopic pregnancy rate were compared between the two groups. Results The number of embryos transferred in fresh embryo transfer group was 2.1±0.4 and FET group was 2.1±0.5 (P 0.05). The rate of multiple births in the fresh group of 3 embryos (80.0%) was higher than that in the FET group (29.7%, P<0.05). In the transplantation group, fresh embryos of different multiple fetal rate differences (P<0.05), FET group of different number of transferred embryos on pregnancy rate and abortion rate differed (P<0.05). The number of transplanted embryos were used as covariates, and the results were analyzed by Logistics regression model. There was no significant correlation between cycle type and clinical pregnancy rate (OR=0.726, 95% CI=0.504-1.104). Conclusion The pregnancy outcomes are similar in patients with endometrial thickness≤7 mm between fresh embryo transfer group and FET group. Choosing fresh embryo transfer cycles does not affect the outcome of pregnancy, can shorten the treatment cycle, and reduce the total cost. Key words: Thin endometrium; Fresh embryo transplantation; Embryo transfer number; Number of transferred embryos; Pregnancy rate