Comparison of subchorionic hematoma in medicated or natural single euploid frozen embryo transfer cycles

To study the effect of frozen embryo transfer (FET) preparation protocol on incidence of subchorionic hematoma (SCH) and serum hormone levels.Retrospective cohort study.University-affiliated fertility center.Patients who underwent FET at the New York University Langone Fertility Center.None.The primary outcome was incidence of SCH by protocol in FET cycles.There were 1,273 FET cycles that met criteria for inclusion. The frequency of SCH was lower in natural compared with programmed cycles (P.05; relative risk = 0.4 [0.27-0.78]; odds ratio = 0.4 [0.23-0.75]). Serum estrogen level was higher in programmed compared with natural cycles on day of progesterone initiation (P.001) and cycle day 28 (P.001). However, serum estrogen levels at the same time points were not associated with formation of SCH in programmed or natural cycles.This is the first study to evaluate the formation of SCHs by FET protocol type. Our results highlight that high serum estradiol levels do not independently lead to an increase in rate of SCH. Further research must be done to understand other clinical, or perhaps molecular, differences between natural and programmed FET cycle preparations that can be better associated with SCH formation.