The entire range of trigger-day endometrial thickness in fresh IVF cycles is independently correlated with live birth rate

What is the association of the entire range of trigger-day endometrial thickness (EMT) with live birth rate (LBR) after IVF and fresh embryo transfer? Although EMT is amenable to convenient non-invasive routine measurement, studies of the association between pre-trigger EMT and assisted reproductive technology outcome have yielded equivocal results.

A cohort of IVF fresh day-3 embryo transfers in patients aged 42 years and younger in a single centre between 2009 and 2017. The LBR was calculated for all trigger-day EMT values, stratified into five groups overall and within subgroups of patient age and ovarian response. Univariate analysis and multivariate logistic regression models were used to compare the LBRs at different EMT measurements adjusting for various independent variables.

A total of 5133 cycles were included. The LBRs were as follows: 11.22% (35/312) in cycles with EMT 6 mm or less, 17.98% (380/2114) in cycles with EMT 7-9 mm, 23.44% (476/2031) in cycles with EMT 10-12 mm, 25.62% (144/562) in cycles with EMT 13-15 mm and 34.21% (39/114) in cycles with EMT 16 mm or more (P < 0.001). Similar findings were observed by patient age and ovarian response. The observation was confirmed by multivariate logistic regression analysis in which the EMT was found to be a significant independent predictor of LBR even after controlling for various confounders (OR 0.935, 95% CI 0.908 to 0.962; P < 0.001).

Pre-trigger EMT is in significant independent correlation with LBR, even after adjusting for age and ovarian response. Maximal endometrial proliferation is beneficial, and fresh embryo transfer can be carried out at high EMT values without endangering the outcome of the cycle.