A comparison of sonographic cervical parameters in predicting spontaneous preterm birth in high-risk singleton gestations

Objectives To assess the role of cervical sonography and to compare various sonographic cervical parameters in their ability to predict spontaneous pr eterm birth in high-risk singleton gestations. Design A prospective cohort of 469 high-risk gestations were longitudinally evaluated between 15 and 24 weeks' gestation on 1265 occasions with transv aginal cervical sonography and transfundal pressure. The cervical parameter s obtained were funnel width and length, cervical length, percent funneling and cervical index. The information obtained was used for patient manageme nt. Restriction of physical activities was initiated at cervical lengths of less than or equal to 2.5 cm with cerclage as an option for cervical lengt hs of less than or equal to 2.0 cm. Results Receiver operating characteristic curve analyses showed that a cerv ical length of : 2.S cm between 1 S and 24 weeks' gestation was equal to th e other sonographic cervical parameters in its ability to predict spontaneo us preterm birth. The sensitivities for delivery at < 28, < 30, < 32 and < 34 weeks' gestation were 94%, 91%, 83% and 76%, respectively, while the neg ative predictive values were 99%, 99%, 98% and 96%, respectively. The place ment of a cerclage did not influence the positive and negative predictive v alues. In comparison to women with other risk factors, cervical length was best in the prediction of Preterm birth in women with a prior mid-trimester loss; an optimal cut-off of less than or equal to 1.5 cm had sensitivities for delivery at < 28, < 30, < 32 and < 34 weeks'gestation of 100%, 100% 92 % and 81%, respectively. The rate of preterm delivery at < 34 weeks' gestat ion increased dramatically when the cervical length was <less than or equal to> 1.5 cm. Cervical length was the only independent variable that entered the logistic regression model for the prediction of preterm delivery at < 34 weeks' gestation. Conclusions In high-risk singleton gestations a cervical length of <less th an or equal to> 2.5 cm was equal to other sonographic cervical parameters i n its ability to predict spontaneous preterm birth and was better for the p rediction of earlier forms of prematurity (at < 28 and < 30 weeks) than lat er forms (at < 32 and < 34 weeks). The optimal cervical lengths and their p erformance for predicting prematurity may be influenced by obstetric risk f actors.