Fresh versus frozen embryo transfer in women with thin endometrium: a retrospective cohort study

BACKGROUND: A thin endometrium affects embryo implantation. We designed a retrospective cohort study to analyze the differences of in vitro fertilization-intracytoplasmic sperm injection (IVF-ICSI) outcomes between fresh embryo transfer (ET) and frozen ET in patients with a thin endometrium. METHODS: The present study comprised of 1,110 patients with a thin endometrium undergoing IVF-ICSI between January 2013 and December 2017 in our unit. Propensity score matching (PSM) was used to balance the influence of intergroup confounding factors and to compare the pregnancy outcomes of the matched patients in the two groups. The fresh embryo group and frozen embryo group consisted of 632 and 478 women, respectively. After PSM, 173 patients were included in the two groups, respectively. RESULTS: The frozen embryo group showed a higher live birth rate (31% vs. 18.4%, P<0.001; 30.6% vs. 19.7%, P=0.019), clinical pregnancy rate (40% vs. 26.4%, P<0.001; 38.7% vs. 25.4%, P=0.008), and biochemical pregnancy rate (46.2% vs. 32.9%, P<0.001; 44.5% vs. 31.8%, P=0.020) than the fresh embryo group before and after PSM. CONCLUSIONS: Our results demonstrated that for women with a thin endometrium who were undergoing IVF, the live birth rate, clinical pregnancy rate, and biochemical pregnancy rate after frozen ET were significantly higher than in the fresh ET group.