P369: Ultrasound cervical length to predict spontaneous preterm delivery in twin pregnancies

Objective: To analyse the predictive value of different cervical length cut-offs for spontaneous preterm delivery <32 and <34 weeks in twin pregnancies. Methods: Transvaginal cervical ultrasound examinations were performed in 106 twin pregnancies between 20 and 26.6 weeks (January 2001 to January 2003). Sensitivity, specificity and predictive values of cervical length (20, 25 mm) at 20–24 and 24.1–26.6 weeks for the prediction of spontaneous preterm birth <32 and <34 weeks were calculated. Twin gestations electively delivered preterm because of maternal or fetal indications were excluded from this analysis. Results: The median gestational age at delivery was 35 weeks (range 23.2–39.3). Cerclage was performed in 12 patients with cervical length 25 mm or prolapse of membranes at a median gestational age of 23 weeks (range 20.5–26.2). The rate of spontaneous delivery <32 and <34 weeks was 8.4% (9/106) and 13.2% (14/106) respectively. In the group of patients evaluated at 20–24 weeks, 7/85 (8.2%) women delivered spontaneously <32 weeks and 9/85 (10.6%) <34 weeks; in the group of patients evaluated at 24.2–26.6 weeks, 2/66 (3%) delivered spontaneously <32 weeks and 7/66 (10.6%) <34 weeks. Cervical length at 20–24 weeks with a cut-off value 20 mm had specificities of 99% and 99%, sensitivities of 43% and 33%, negative predictive values of 95% and 92%, positive predictive values of 75% and 75% for delivery <32 and <34 weeks, respectively. Cervical length at 20–24 weeks with a cut-off value 25 mm had specificities of 95% and 94%, sensitivities of 43% and 33%, negative predictive values of 95% and 91%, positive predictive values of 43% and 43% for delivery <32 and <34 weeks, respectively. Conclusions: In twin gestations a cervical length 20 mm measured at 20–24 weeks is the best cut-off to predict spontaneous preterm delivery.