Effect of uterine dimensions on live birth rates after single embryo transfer in infertile women

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 first SET between August 2010 and March 2014 at a large university hospital reproductive centre. The effects of baseline uterine dimensions on live birth rate (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/m²; P = 0.015) and a higher number of fibroids (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 significant 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 significantly 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 LBR 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.