LAUSR

Study Objective To investigate the association between uterine size and pregnancy outcomes in IVF cycles. Design Retrospective cohort study. Setting University-affiliated fertility center. Patients or Participants Women with primary infertility Interventions Fresh ET. Measurements and Main Results Uterine volume was used as a surrogate for uterine size. Uterine measurements (length, width, thickness) were obtained in each woman. Uterine volume was calculated using the prolate ellipsoid volume formula (V=0.52 x L x W x T). Baseline demographics, IVF cycle characteristics and perinatal outcomes were measured. Term birth, defined by live birth >37 weeks of gestation was considered the primary outcome of interest. The odds of pre-term and term birth were estimated in each uterine volume quartile. A receiving-operator-characteristic (ROC) curve with a corresponding area-under-the-curve (AUC) was generated to assess the performance of uterine volume as predictor of term birth. The study included 261 patients with live singleton births. The median (IQR) age, height, weight, body mass index (BMI) and uterine volume for the study cohort was 34 (31-39) years, 163 (160-167) cm, 137 (122-155) lbs, 22.1 (20.3-24.9) kg/m2 and 55.5 (43.2-67.9) mL, respectively. The rates of term birth and pre-term birth were 224/261(85.8%) and 37/261 (14.2%). There was no difference in the baseline demographics or IVF cycle characteristics of women with term birth or pre-term births. The overall odds of term birth increased with uterine volume. Specifically, the odds of term birth in 4th quartile (highest uterine volume) were 3.4 (95% CI 2.1-7.4; P=0.01) times higher than the 1st quartile. Uterine volume was found to be a strong predictor of term birth (AUC=0.87). Conclusion Our findings suggest that baseline uterine volume is a strong predictor of term birth after fresh ET. These findings require prospective validation in larger sample sizes given the multifactorial nature of term birth.