Increasing Endometrial Thickness up to 12mm Is Associated with Increased Odds of Live Birth Among Fresh and Frozen-Thawed Autologous Transfers with or without PGT.

OBJECTIVE To evaluate the impact of endometrial thickness on live birth among autologous assisted reproduction cycles. DESIGN Retrospective cohort SUBJECTS: All women undergoing autologous cycles with transfers in 2016-2018 reported to the Society for Assisted Reproductive Technology. EXPOSURE Endometrial thickness on the day of ovulation trigger in fresh cycles and closest to embryo transfer in frozen-thawed cycles MAIN OUTCOME MEASURES: Relative risk of live birth across endometrial thicknesses was compared with an 8-11.9mm reference range. Estimates were adjusted for age, BMI, smoking, infertility etiology, AMH and FSH with log-binomial regression by generalized estimating equations. Fresh transfers, frozen-thawed transfers without preimplantation genetic testing and frozen-thawed transfers with preimplantation genetic testing were analyzed separately. RESULTS 182,784 patients underwent 261,266 combined retrieval and transfer cycles. Patients with endometrium <8mm were slightly older, with lower BMI, higher rates of prior pregnancy loss, diminished ovarian reserve and ovulation disorders besides polycystic ovarian syndrome but lower rates of male or unexplained infertility. When all fresh and frozen-thawed transfers were combined, live birth rate increased with endometrial thickness from 31.2% (<6mm) to 34.4% (6-6.9mm) to 40.8% (7-7.9mm) to 45.0% (8-11.9mm) to 46.4% (12-14.9mm) to 46.2% (≥15mm). For fresh cycles without preimplantation genetic testing, thinner endometrium was associated with reduced live birth rate compared with the 8-11.9mm reference range (adjusted relative risk 0.59 (95% CI 0.48-0.72), 0.66 (0.58-0.74), 0.79 (0.74-0.84) for thickness <6mm, 6-6.9mm and 7-7.9mm), while 12-14.9mm and ≥15mm thickness were associated with increased live birth rate (adjusted relative risk 1.12 (1.09-1.15) and 1.16 (1.12-1.22)). Similar but less dramatic effects were noted for frozen-thawed cycles without preimplantation genetic testing (adjusted relative risk 0.87 (0.77-0.99), 0.79 (0.73-0.85), 0.94 (0.91-0.97), 1.06 (1.03-1.08) and 1.04 (0.98-1.1) for thickness <6mm, 6-6.9mm, 7-7.9mm, 12-14.9mm, and ≥15mm) and frozen-thawed cycles with preimplantation genetic testing (adjusted relative risk 0.67 (0.59-0.77), 0.80 (0.76-0.85), 0.89 (0.87-0.92), 1.07 (1.05-1.1), and 1.06 (1-1.11) for thickness <6mm, 6-6.9mm, 7-7.9mm, and 12-14.9mm and ≥15mm). CONCLUSION Increasing endometrial thickness from 5 to 8mm is associated with clear increases in live birth rate, but improvements are still seen until approximately 12mm, including frozen-thawed cycles with preimplantation genetic testing.