Transvaginal ultrasound in the prediction of preterm delivery: singleton and twin gestations

To compare, in singleton and twin pregnancies, the effectiveness of transvaginal ultrasound versus digital examination in predicting preterm delivery in women with suspected preterm labor.

Transvaginal ultrasound and pelvic examinations were performed on patients admitted with suspected preterm labor between 23 and 33 weeks' gestation. Ultrasound assessment of cervical length and the presence of funneling with fundal pressure were recorded for each patient, and the results were compared with dilatation and effacement as assessed by digital examination for the prediction of preterm delivery in the two groups (singletons and twins).

One hundred sixty-two subjects were recruited (136 singletons and 26 twin pregnancies), with no significant demographic differences between the groups. Overall, 33% of the participants delivered preterm (27% of singletons, 62% of twins). Using receiver operating characteristics curves, the best cutoff points were 30 mm for endocervical length at ultrasound, 50% for effacement, and 1.5 cm for dilatation. Of these, the best predictor was endocervical length, which was a better predictor in singleton than in twin pregnancies. Of the potential predictors, including endocervical length, funneling, dilatation, and effacement, only endocervical length was an independent predictor of preterm delivery at less than 34 weeks' gestation for both singletons and twins by multiple logistic regression. When analyzed for delivery at less than 37 weeks' gestation, this relation held true for singletons but not twins. Endocervical length less than 30 mm had a sensitivity of 81% and 75%, specificity of 65% and 30%, positive predictive value of 46% and 63%, and negative predictive value of 90% and 43% for singleton and twin pregnancies, respectively, in predicting spontaneous birth at less than 37 weeks' gestation.

Between 23 and 33 weeks' gestation, transvaginal ultrasound assessment of endocervical length is superior to funneling and digital examination in predicting preterm delivery in patients who present with suspected preterm labor, and is a better predictor in singletons than in twins.