Effect of transdermal estrogen dose regimen for endometrial preparation of frozen‐thawed embryo transfer on reproductive and obstetric outcomes

PURPOSE: Previous studies have reported different methods of estrogen administration during endometrial preparation for frozen‐thawed embryo transfer (FET). This study aimed to investigate a beneficial regimen of transdermal estrogen administration for FET. METHODS: We investigated the reproductive and obstetric outcomes of FET by comparing the increasing dose (ID) group that mimics changes in serum estradiol during the menstrual cycle and the constant dose (CD) group. Transdermal patches were used for estrogen administration in both groups. In our hospital, we targeted 315 cycles of the ID group in which FET was performed in 2017 and 324 cycles of the CD group in which FET was performed in 2018. In all cases, single embryo transfer was performed. RESULTS: All were singleton pregnancies. There was no difference in clinical pregnancy rate (28.9% vs 28.2%, P =.837) and live birth rate (17.3% vs 21.4%, P =.201) between the ID and CD groups. Spontaneous abortion rate was significantly lower in the CD group than in the ID group (37.2% vs 23.0%, P =.041). There was no difference in obstetrical outcomes. CONCLUSIONS: It was considered that the simple CD regimen may be more beneficial than the complicated ID regimen.