Abstract
Background: The need for endocrine monitoring in artificial cycles for frozen embryo transfer (FET) remains unclear and, more specifically, the value of the late-proliferative phase serum estradiol (E2) levels is with conflicting evidence in current literature.Objective: To investigate whether artificial FET cycles require endocrine monitoring for the serum E2 level prior to initiation of exogenous progesterone administration after an endometrial thickness of 6.5 mm has been reached.Design: One thousand two hundred and twenty-two (n = 1,222) artificial FETs performed in a tertiary center between 2010 and 2015 were subdivided into 3 groups according to the following late-proliferative serum E2 level percentiles: ≤p10 (E2 ≤144 pg/ml; n = 124), p11–p90 (E2 from 145 to 438 pg/ml; n = 977) and >p90 (E2 >439 pg/ml; n = 121).A mixed-effects multilevel multivariable regression analysis was performed to assess the potential effect of the late-proliferative E2 level on the live birth rate (LBR).Results: The level of late-proliferative circulating E2 showed no significant difference in terms of LBR after FET. Specifically, the multivariable regression model demonstrated a LBR of 19.5% for the p11–p90 reference group, compared to 24.4% for the ≤p10 (p = 0.251) and 19.5% for the >p90 group (p = 0.989).Conclusion: In this large retrospective dataset, no association was observed between late-proliferative phase serum E2 levels and LBR following FET in artificially prepared cycles. Although, caution is warranted due to the retrospective nature of the analysis and the potential for unmeasured confounding, we argue that monitoring of the late-proliferative serum E2 levels and using them to guide clinical decision-making (e.g., medication step-up, cycle prolongation or cancelation) may be of questionable value.
Highlights
The use of frozen embryo transfer (FET) has progressively increased, it is still unknown whether a specific endometrial preparation protocol should be favored over another (1, 2)
A total of 854 patients were included in the analysis having performed 1,222 artificial autologous FET cycles
Unexplained infertility was more frequent in the p ≤ 10 group and the rank of the fresh cycle was significantly higher in the p > 90 group
Summary
The use of FET has progressively increased, it is still unknown whether a specific endometrial preparation protocol should be favored over another (1, 2). Luteinizing hormone (LH) levels frequently rise in the proliferative phase of artificial cycles without pituitary suppression simulating that what occurs prior to a natural cycle ovulation. In this specific setting, the LH levels are no indicators for the phenomenon as a priori the estrogen (E2) supplementation suppresses follicular development (3, 4). The need for endocrine monitoring in artificial cycles for frozen embryo transfer (FET) remains unclear and, the value of the late-proliferative phase serum estradiol (E2) levels is with conflicting evidence in current literature
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