Cervical length at mid‐gestation in screening for preterm birth in twin pregnancy. (5th July 2016) - Pagani, G.
Abstract: Objective: Short cervical length (CL) in mid‐gestation is considered predictive of spontaneous preterm birth (PTB). The medical literature suggests 20 mm as the cut‐off for high risk in twin pregnancies. Our objective was to assess the predictive value of CL for spontaneous PTB < 32 weeks' gestation in twin pregnancies and to calculate the cut‐off point with the best sensitivity and specificity. Methods: This was a single‐center retrospective cohort study of women in whom CL had been measured by transvaginal ultrasound at 18–23 weeks' gestation. Pregnancies complicated by twin‐to‐twin transfusion syndrome, those requiring intrauterine therapy or those with indicated PTB were excluded. The predictive value of CL for PTB < 32 weeks was assessed. The distribution of CL measurements and the optimal cut‐off in patients with PTB were calculated and logistic regression analysis was performed to assess the association between pregnancy characteristics and PTB. Results: A total of 940 twin pregnancies were included. CL showed an area under the receiver–operating characteristics curve of 0.65 (95% CI, 0.58–0.71) for the prediction of PTB < 32 weeks. The optimal cut‐off value for predicting PTB was 36 mm (sensitivity, 64.1%; specificity, 62.8%; positive predictive value, 13.5%; negative predictive value, 95.1%; accuracy, 62.9%). The relative risk of PTB with CL ≤ 36 mm was 2.35 (95% CI, 1.53–3.60; P < 0.001). After adjusting for confounders in logistic regression analysis, only CL (adjusted odds ratio (aOR), 0.94 (95% CI, 0.90–0.99); P = 0.03), and not monochorionicity (aOR 4.14 (95% CI, 0.89–19.25); P = 0.07), was independently associated with PTB. More than one‐third (36%) of PTB cases delivering < 32 weeks had a normal CL in mid‐gestation. This proportion rose to 85% when considering the 20‐mm cut‐off suggested by the medical literature. Conclusions: This study shows that, despite the weak independent association, CL assessed in mid‐gestation is a poor predictor of PTB < 32 weeks' gestation in asymptomatic twin pregnancies. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.