Preterm Birth Risk in Women with Uterine Anomalies

OBJECTIVE: To evaluate preterm birth rate and pregnancy outcomes in women with and without congenital uterine anomalies. STUDY DESIGN: We performed a retrospective observational matched-cohort study of 674 nulliparous women with and without uterine anomalies delivering a live birth in Kaiser Permanente Northern California between 2009-2016. Women with uterine anomalies (n=337) (didelphys, septate, bicornuate, unicornuate) were compared to 337 women without uterine anomalies. Primary outcome was preterm birth (PTB). Secondary outcomes were preterm premature rupture of membranes (PPROM), small for gestational age (SGA), cesarean delivery, and postpartum hemorrhage. RESULTS: The incidence of PTB < 37 weeks and PTB < 34 weeks in women with uterine anomalies was 23.7% and 8%, respectively. As compared to women without uterine anomalies, women with a uterine anomaly had an increased risk of PTB < 37 weeks (odds ratio [OR] 4.1; 95% confidence interval [CI] 2.5-6.6; p<0.01), PTB < 34 weeks (OR 4.8; 95% CI 2.0-11.8; p<0.01), PPROM (OR 4.7; 95% CI 2.3-9.4; p<0.01), cesarean delivery (OR 3.0; 95% CI 2.2-4.2; p<0.01), and malpresentation (OR 9.0; 95% CI 5.4-15.1; p<0.01). There was a low incidence of PTB < 28 weeks in both groups (1.8% cases vs. 0.3% controls; p=0.1). Compared to women without uterine anomalies, women with a uterine anomaly showed a tendency towards increased risk of postpartum hemorrhage (OR 2.8; 95% CI 0.9-8.9; p=0.07) and SGA (OR 1.5; 95% CI 1.0-2.4; p=0.06). There were no hysterectomies. The diagnosis of uterine anomaly was confirmed in 69% of the subjects by cesarean, MRI, or laparoscopy; 2D ultrasound alone was used to make the diagnosis in 25% of subjects. CONCLUSION: Women with a uterine anomaly are at increased risk of preterm birth and adverse pregnancy outcomes, but most women deliver at term. This is the largest study to date of pregnancy outcomes in women with uterine anomalies with most anomalies confirmed by a reliable method of diagnosis.