Objective: Women with uterine anomalies have higher rates of preterm birth, but the reason for this has not been elucidated. Transvaginal ultrasound examination has been shown to be an accurate test for the prediction of preterm birth but has not been studied specifically in this population. Methods: Pregnant women with uterine anomalies were followed prospectively with transvaginal ultrasound examination of the cervix, performed between 14 and 23 6/7 weeks of gestation. A short cervical length was defined as less than 25 mm of cervical length. The primary outcome was spontaneous preterm birth, defined as birth at less than 35 weeks. Results: Of the 64 pregnancies available for analysis, there were 28 with a bicornuate uterus, 13 with a septate uterus, 11 with a uterine didelphys, and 12 with a unicornuate uterus. The overall incidence of spontaneous preterm birth at less than 35 weeks was 11%. Of the 10 (16%) women with a short cervical length, 5 (50%) had spontaneous preterm birth. Of the 54 women without a short cervical length, only 2 (4%) had a spontaneous preterm birth. The sensitivity, specificity, and positive and negative predictive values of a short cervical length for spontaneous preterm birth were 71%, 91%, 50%, and 96%, respectively (relative risk 13.5, 95%confidence interval 3.49-54.74). Of the 7 women with both short cervical length and preterm birth,all uterine subtypes were represented except septate uterus. Conclusion: A short cervical length on transvaginal ultrasonography in women with uterine anomalies has a 13-fold risk for preterm birth. Unicornuate uterus had the highest rate of cervical shortening and preterm delivery. Objective: Women with uterine anomalies have higher rates of preterm birth, but the reason for this has not been elucidated. Transvaginal ultrasound examination has been shown to be an accurate test for the prediction of preterm birth but has not been studied specifically in this population. Methods: Pregnant women with uterine anomalies were attended prospectively with transvaginal ultrasound examination of the cervix, performed between 14 and 23 6/7 weeks of gestation. A short cervical length was defined as less than 25 mm of cervical length. The primary outcome was spontaneous Preterm birth, defined as birth at less than 35 weeks. Results: Of the 64 pregnancies available for analysis, there were 28 with a bicornuate uterus, 13 with a septate uterus, 11 with a uterine didelphys, and 12 with a unicornuate uterus. overall incidence of spontaneous preterm birth at less than 35 weeks was 11%. Of the 10 (16%) women with a short cervical length, 5 (50%) had spontaneous preterm birth. O The sensitivity, specificity, and positive and negative predictive values ​​of a short cervical length for spontaneous preterm birth were 71%, 91%, 50 %, and 96% respectively (relative risk 13.5, 95% confidence interval 3.49-54.74). Of the 7 women with both short cervical length and preterm birth, all uterine subtypes were represented except septate uterus. transvaginal ultrasonography in women with uterine anomalies has a 13-fold risk for preterm birth. Unicornuate uterus had the highest rate of cervical shortening and preterm delivery.