Comparison of live birth rates following the transfer of day-6 blastocysts on the 6th versus 7th day of progesterone exposure in hormone replacement treatment-frozen embryo transfer cycles.

Objective: The duration of progesterone exposure is critical for establishing and maintaining a pregnancy in hormone replacement treatment (HRT)-frozen embryo transfer (FET) cycles. This study compared the live birth rates (LBRs) of patients undergoing day-6 warmed blastocyst transfer on either the 6th or 7th day of progesterone administration in HRT-FET cycles.

Methods: A retrospective cohort study was conducted using data from the central registry of Indira IVF Hospital Private Limited. In total, 2,633 patients who underwent day-6 blastocyst transfer cycles with HRT-FET were identified. The cycles were categorized based on the timing of the day-6 blastocysts transfer: P+6 vs. P+7 (initiation date: P+1). Propensity scores were calculated. The primary outcome measure was the LBR.

Results: Following propensity score matching, a total of 1,401 patients were included in the final analysis (P+6: n=1,212; P+7: n=189). The number of previous attempts was significantly higher in the P+6 group, whereas the rate of preimplantation genetic testing for aneuploidy was significantly higher in the P+7 group. The LBRs were 59.2% and 54.5% in the P+6 and P+7 groups, respectively (p=0.21). Multivariate regression analysis revealed that the number of previous in vitro fertilization attempts (odds ratio [OR], 3.246; 95% confidence interval [CI], 2.429 to 4.337; p<0.001), the number of blastocysts transferred (OR, 2.011; 95% CI, 1.461 to 2.768; p<0.01), and endometrial thickness on the day of progesterone initiation (OR, 1.143; 95% CI, 1.022 to 1.28; p=0.02) were independent predictors of live birth.

Conclusions: The LBRs were comparable in patients who underwent day-6 warmed blastocyst transfer on day 6 or 7 post-progesterone initiation in HRT-FET cycles.