Cleavage-stage embryo transfer cycles and blastocyst-stage embryo transfer cycles were analyzed separately and then compared in this study because the age of the transferred embryo is an important factor affecting the success rate of implantation. To eliminate bias due to the effects of other variables on embryonic implantation, the present retrospective study analyzed frozen-thawed transfer cycles with two good-quality embryos transferred into the normal uterus of patients under 40 years of age with an endometrial thickness of at least 7 mm on the progesterone initiation day. In addition to synchronization between endometrial maturation and transferred embryos, female age, the uterine condition, and embryonic factors are known as major variables affecting embryo implantation. The discrepant findings may be due to the different patient populations recruited, differences in the protocols used for endometrial preparation, and differences in the day in which steroid hormone levels were measured between studies. demonstrated that elevated E 2 levels in artificial FET cycles were related to a low ongoing pregnancy/live birth (OP/LB) rate 8, but some authors did not observe this association 9, 10, 11. There is limited available information regarding the need for endocrine monitoring during hormone replacement therapy (HRT), although supplementation with steroid hormones is necessary for endometrial preparation. Moreover, excess E 2 levels have been found to increase the incidence of abnormal pregnancy conditions, such as intrauterine growth restriction and abnormal implantation of the placenta 6, 7. In fresh cycles, excess E 2 has been shown to be detrimental to endometrial development and to ultimately adversely affect conception 4, 5. Undoubtedly, estradiol (E 2) coordinately interacts with progesterone and plays an important role in endometrial development 2, 3.
However, it is not necessary to monitor E 2 levels when transferring blastocysts in artificial FET cycles.Įndometrial preparation is a critical step in both the natural and artificial frozen embryo transfer (FET) cycle because the development of the endometrium must be synchronized with the embryo transfer for successful implantation 1. The results suggests that elevated progesterone-initiation-day E 2 levels may negatively affect pregnancy outcomes during artificial cleavage-stage embryo transfers. However, in blastocyst-stage embryo transfers, such trends were not observed, and E 2 levels were not significant difference between the OP/LB group and the non-OP/LB group (201.66 ± 182.14 vs.
In addition, there were downward trends in implantation, clinical pregnancy and OP/LB rates with increasing E 2 levels. Regarding cleavage-stage embryo transfers, E 2 levels on progesterone initiation day were significantly lower in the ongoing pregnancy/live birth (OP/LB) group than in the non-OP/LB group (214.75 ± 173.47 vs. A total of 776 FET cycles (669 couples) performed from January 2016 to December 2019 were included in the present retrospective cohort study. This study was to compare the effects of serum E 2 levels on pregnancy outcomes between cleavage- and blastocyst-stage FET cycles using hormone replacement therapy. Supplementation with estradiol (E 2) is routinely used in frozen embryo transfer (FET) cycles and embryo age plays an important role in conceiving.
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