Optimal duration of progesterone before cryopreserved embryo transfer in hormone replacement therapy cycles: A prospective pilot study

This prospective pilot cohort study aimed to ascertain the optimal duration of progesterone supplementation prior to frozen embryo transfer (FET) in women undergoing hormone replacement therapy (HRT) cycles. A total of 127 participants were enrolled and divided into 2 cohorts. The first cohort, comprising of 39 women, was used to determine the peak period of endometrial receptivity. These participants underwent serial assessments of integrin alphavbeta3, homeobox gene A10, and leukemia inhibitory expression levels from days 3 to 7 (P + 3 to P + 7) during the mock HRT cycles. The second cohort included 88 women who embarked on their inaugural HRT-FET cycle and were monitored for pregnancy outcomes after the transfer of D3 embryos after 3 or 4 days of progesterone administration. The results indicated a significant enhancement in biochemical pregnancy and embryo implantation rates in the P + 3 group (87.18% and 74.36%, respectively) compared to those in the P + 4 group (68.42% and 65.79%; P = .047 and P = .044, respectively). These data suggest that a 3-day progesterone regimen prior to D3 embryo transfer may be more beneficial. Notably, the maximal expression of endometrial receptivity markers was observed on day P + 6 within the HRT cycles, which is consistent with previous research that correlated day 6 embryos with peak endometrial receptivity. Therefore, a 3-day progesterone lead-in may enhance synchrony between D3 embryos and the endometrium. Our findings suggest that initiating D3 embryo transfer after 3 days of progesterone administration may optimize embryo-endometrial synchronization, thereby potentially enhancing clinical outcomes in FET cycles.