OBJECTIVE

This study was undertaken to compare various ultrasonographic cervical parameters with respect to ability to predict spontaneous preterm birth in twin gestations.

STUDY DESIGN

This prospective study involved 131 women carrying twins who were longitudinally evaluated on 524 occasions between 15 and 28 weeks' gestation with transvaginal cervical ultrasonography and transfundal pressure. The following cervical parameters were obtained: funnel width and length, cervical length, percentage of funneling, and cervical index. Receiver operating characteristic curve analysis was used to determine the ultrasonographic cervical parameter evaluated at 15 to 20 weeks' gestation, 21 to 24 weeks' gestation, and 25 to 28 weeks' gestation that were best for prediction of spontaneous preterm birth at <28 weeks' gestation, <30 weeks' gestation, <32 weeks' gestation, and <34 weeks' gestation.

RESULTS

The median gestational age at delivery was 36 weeks' gestation (range, 21-41 weeks' gestation). Receiver operating characteristic curve analysis indicted that a cervical length of < or =2.0 cm, regardless of gestational age category at cervical measurement, was at least as good as other ultrasonographic cervical parameters at predicting spontaneous preterm birth. Between 15 and 20 weeks' gestation a cervical length cutoff value of < or =2.0 cm had specificities of 97%, 98%, 99%, and 100% and negative predictive values of 99%, 98%, 95%, and 89% for delivery at <28, <30, <32, and <34 weeks' gestation, respectively. The positive predictive values for delivery at <32 and <34 weeks' gestation were 80% and 100%, respectively. Between 21 and 24 weeks' gestation a cervical length of < or =2.0 cm had specificities of 84%, 84%, 85%, and 86% and negative predictive values of 99%, 99%, 94%, and 87% for delivery at <28, <30, <32, and <34 weeks' gestation, respectively. Between 25 and 28 weeks' gestation cervical length had excellent negative predictive values of 99%, 98%, 95%, and 93% for delivery at <28, <30, <32, and <34 weeks' gestation, respectively.

CONCLUSIONS

In twin gestations a cervical length of < or =2.0 cm measured between 15 and 28 weeks' gestation was at least as good as other ultrasonographic cervical parameters at predicting spontaneous preterm birth. The high specificities indicate that cervical length was better at predicting the absence than the presence of various degrees of spontaneous prematurity.