1 RBMO VOLUME 00 ISSUE 0 2020 1 Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology and Infertility, McGill University, Montreal QC, Canada 2 MUHC Reproductive Centre, McGill University Health Centre, Montreal QC, Canada © 2020 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved. *Corresponding author. E-mail address: naama.steiner@mail.mcgill.ca (N Steiner). https://doi.org/10.1016/j. rbmo.2020.07.007 1472-6483/© 2020 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved. Declaration: The authors report no fnancial or commercial conficts of interest. KEYWORDS IVF Single embryo transfer Uterine dimensions ARTICLE Effect of uterine dimensions on live birth rates after single embryo transfer in infertile women BIOGRAPHY Naama Steiner received her medical degree from the Ben-Gurion University (BGU) and completed OB/GYN residency training at the Soroka University Medical Center, Beer- Sheva, Israel. She is currently doing postgraduate training in reproductive endocrinology and infertility at McGill University, Canada. Naama Steiner 1,2, *, Senem Ates 1 , Talya Shaulov 1 , Samer Tannus 1 , Michael H. Dahan 1,2 KEY MESSAGE Uterine parameters, particularly uterine length and cervical length, are statistically associated with live birth outcomes from IVF. However, due to signifcant variability and low levels of predictability by ROC curves, uterine parameters are not clinically useful. ABSTRACT Research question: Do uterine size parameters measured by baseline transvaginal ultrasound predict live birth after single embryo transfer (SET) of a high-quality blastocyst? Design: Retrospective cohort study including women undergoing their frst SET between August 2010 and March 2014 at a large university hospital reproductive centre. The effects of baseline uterine dimensions on live birth rates (LBR) were analysed while controlling for confounding effects. Results: A total of 437 nulliparous and 70 parous women were included. The nulliparous group had lower body mass index (BMI) (24.4 ± 5.1 versus 25.9 ± 4.5 kg/m 2 ; P = 0.015) and a higher number of fbroids (0.4 ± 1.0 versus 0.2 ± 0.5; P = 0.005) than the parous group. While controlling for confounding effects, none of the uterine parameters appeared to be a signifcant predictor of LBR among nulliparous and parous women (P > 0.05 in all cases). A subsequent analysis of endometrial length was done, whereby the endometrial lengths were divided into quartiles (20.0–32.2 mm; 32.3–36.5 mm; 36.6–40.0 mm; 40.1–54.0 mm). After controlling for confounders, the shortest quartile in the nulliparous group had a signifcantly lower LBR (P = 0.02) than the other groups. Receiver operating characteristic curves suggested that endometrial cavity length and cervical length did not aid clinically. Conclusion: Uterine parameters do not have a clinically useful impact on LBRs after SET of a blastocyst in infertile women. The use of baseline endometrial length to predict live birth is no better than chance, while cervical length only predicts failure to live birth. Q1