Impact of the duration of oestradiol treatment on live birth rate in Hormonal Replacement Therapy cycle before frozen blastocyst transfer.

Although the duration of progesterone administration in Hormonal Replacement Therapy (HRT) cycles before frozen embryo transfer is standardized, the optimal duration of oestrogen treatment remains controversial. In this monocentric retrospective study conducted in all single frozen blastocyst transfer (FBT) performed with HRT between January 2016 and July 2019, we evaluated the association between the duration of oestradiol treatment before FBT and live birth rate (LBR) in HRT cycles. Cycles were gathered in 3 groups according to quartiles of duration of oestrogen treatment. LBR was compared across the 3 groups and multivariate analysis was performed. We included 2235 single FBT cycles; 507, 1257 and 471 with E2 treatment below 23 days, 23-30 days (reference) and more than 30 days respectively. After multivariate analysis and adjustment, no significant difference in LBR was found between below 23 or more than 30 days and reference groups (OR = 0.93 [0.68-1.27] and OR = 1.29 [0.88-1.89] respectively). Complementary sensitivity analysis led to a non-significant adjusted OR = 1.66 [IC 0.9-3.1]. In conclusion, our study showed that the duration of E2 treatment in HRT cycles before FBT is not associated with LBR.