Prediction of preterm delivery with transvaginal ultrasonography of the cervix in patients with high-risk pregnancies: Does cerclage prevent prematurity?

OBJECTIVES: We sought to determine the predictive accuracy for preterm deli very of transvaginal ultrasonography of the cervix between 14 and 24 weeks' gestation in high-risk patients and to determine whether cerclage prevents preterm delivery in patients with ultrasonographic cervical changes. STUDY DESIGN: Patients with asymptomatic singleton pregnancies at high risk for preterm delivery were followed prospectively from 14 weeks' to 23 week s 6 days' gestation with transvaginal ultrasonography of the cervix. The su bgroup of patients with either a cervical length of <25 mm or funneling of >25% or both was offered McDonald salvage cerclage, which was performed at the discretion of the patient and the obstetrician. The 2 groups (with and without cerclage) were compared for the primary outcome of preterm delivery at <35 weeks' gestation. RESULTS: One hundred sixty-eight women were followed, including 97 (58%) wi th greater than or equal to 1 prior 14- to 34-week preterm deliveries. Of 6 3 (37.5%) patients identified as having cervical changes, 23 (37%) had pret erm delivery; of 105 patients with no cervical changes, 8 (8%) had preterm delivery (relative risk, 4.8; 95% confidence interval, 2.3-10.1). The sensi tivity, specificity, and positive and negative predictive valves of either a short cervix of <25 mm or funneling of >25% or both were 74%, 70%, 37%, a nd 92%, respectively. Of 63 pregnancies in which there were cervical change s, 39 underwent cerclage and 24 did not. These 2 groups were similar for de mographic characteristics, risk factors, and transvaginal ultrasonographic cervical length and funneling but dissimilar for gestational age at identif ication of cervical changes (18.3 vs 21.2 weeks' gestation in the groups wi th and without cerclage, respectively; P < .001). Multivariate logistic reg ression analysis after adjustment for gestational age at cervical changes s howed no difference in the rate of preterm delivery between the groups with and without cerclage (odds ratio, 1.1; 95% confidence interval, 0.3-4.6). Stratified analysis of patients identified between 18 and 24 weeks revealed 22 pregnancies with cerclage and 22 pregnancies without cerclage, which wa s similar for all characteristics studied. The incidence of preterm deliver y remained similar (27% vs 23%, respectively; P = .7), as did days from cer vical changes to delivery (111 vs 96, respectively; P = .2). CONCLUSIONS: Transvaginal ultrasonography of the cervix between 14 and 24 w eeks' gestation is a good predictor of preterm delivery in high-risk pregna ncies. Cerclage may not prevent preterm delivery in patients identified to be at high risk for this outcome by transvaginal ultrasonography.