Bourdon M, et al. - Researchers sought to assess the effect of the duration of estrogen (E2) treatment prior to frozen-blastocyst transfers on the live birth rate (LBR). They noted that prolonged E2 exposure (exceeding 28 days) as part of artificial endometrial preparation (AEP) markedly reduced the LBR after autologous frozen–thawed blastocyst transfer. Thus they suggested not exceeding 28 days the length of E2 exposure prior to the frozen-blastocyst transfer to give patients the best chance to obtain a live birth after frozen–thawed blastocyst transfer.

Methods

• Researchers undertook an observational cohort study in a tertiary care university hospital between 01/07/2012 and 31/12/2015.
• For this study, the main inclusion criteria was having a single frozen–thawed blastocyst transfer with an AEP using exogenous E2.
• Based on the duration of the E2 administration prior to the embryo transfers, they assigned a total of 1,377 frozen–thawed blastocyst transfers to four groups: ‘≤21 days’ group (n = 330), ‘22–28 days’ group (n= 665), ‘29–35 days’ group (n = 289) and ‘36–48 days’ group (n = 93).
• They considered the ‘≤21 days’ group’ as the reference group.
• The LBR following frozen–thawed blastocyst transfers was the main measured outcome.
• Using univariate and multivariate logistic regression models, they conducted statistical analysis.

Results

• Significant reduction in LBR was noted when the E2 exposure prior to the frozen–thawed blastocyst transfer exceeded 28 days: OR = 0.66; 95% CI [0.46–0.95]; P=0.026 and OR = 0.49 [0.27–0.89]; P=0.018, respectively, for the ‘29 to 35 days’ group and for the ‘36 to 48 days’ group compared to the reference group.
• In case of E2 exposure lasting more than 35 days prior to the frozen–thawed blastocyst transfer, significantly increased early pregnancy loss rates were noted (OR = 2.37 [1.12–5.05]; P=0.025 vs the reference group).
• Multivariate logistic regression suggested that E2 exposure lasting more than 28 days prior to the frozen–thawed blastocyst transfer was associated with a decrease in the LBR, for the ‘29–35 days’ group (OR = 0.65; [0.45–0.95]; P=0.044) as for the ‘36–48 days’ group (OR = 0.49; [0.26–0.92]; P=0.035), vs the reference group.