Does it affect the live birth rates to have a maximum endometrial thickness of 7, 8, or 9 mm in in-vitro fertilization-embryo transfer cycles?

Objective: To assess the effect of endometrial thickness (EMT) on live birth rates (LBR) in women with endometrial lining between 7.0-9.9 mm.

Methods: This retrospective cohort study included women who underwent fresh and frozen embryo transfers between 2008 and 2018, grouped according to their maximum EMT; group 1, 7.0-7.9 mm; group 2, 8.0-8.9 mm; and group 3, 9.0-9.9 mm and underwent blastocyst transfer.

Results: The study included 7,091 in-vitro fertilization cycles: 1,385 in group 1, 3,000 in group 2, and 2,706 in group 3. The combined LBR was 22.2%. The mean age of women at oocyte retrieval day was 36.7±4.5 years. There was no difference in female age at oocyte retrieval or in the quality of embryos transferred between the three groups. Group 1 had more diagnoses of diminished ovarian reserve (25.8% vs. 19.5% and 19.1%; p<0.001) and less male factor infertility compared with group 2 and 3, respectively (25.0% vs. 28.8% and 28.5%; P=0.024). LBR was higher with increasing endometrial thickness, group 2 vs. group 1 (22.0% vs. 17.4%; P=0.0004), group 3 vs. group 1 (25.0% vs. 17.2%; p<0.001), and group 3 vs. group 2 (25.0% vs. 22.0%; P=0.008). After controlling for confounding factors, these three groups did not differ in LBR (group 1 vs. group 2, odds ratio [OR], 1.08; 95% confidence interval [CI], 0.83-1.4; P=0.54 and group 1 vs. group 3, OR, 1.16; 95% CI, 0.90-1.51; P=0.24).

Conclusion: Live birth rates in women with endometrial thickness between 7.0-9.9 mm were not affected by different cut-offs when blastocyst transfer was performed.