Prediction of prolonged pregnancy in nulliparous women by transvaginal ultrasonographic measurement of cervical length at 20-24 weeks and 37 weeks

Abstract

This study was done to evaluate transvaginal ultrasonographic measurement of cervical length at 20 to 24 weeks and 37 weeks as a predictor of prolonged pregnancy (defined as a pregnancy that extended beyond 41+2 weeks of gestation [289 days]) in nulliparous women. This prospective observational study enrolled 149 consecutive nulliparous women with singleton gestation at 37 weeks. Cervical length was measured by transvaginal ultrasonography at 20 to 24 weeks and 37 weeks. Cervical length at 37 weeks, but not at 20 to 24 weeks, was significantly longer in women delivered at >41+2 weeks than in those delivered at <or=41+2 weeks (p<0.005). There was a significant correlation between cervical length at 37 weeks and gestational age at delivery (Pearson correlation coefficient, r=0.387, p<0.0001). In the receiver operating curve, the best cut-off value of cervical length at 37 weeks for the prediction of prolonged pregnancy was 30 mm, with a sensitivity of 78% and a specificity of 62%. Cervical length assessed by transvaginal ultrasonography at 37 weeks can predict the likelihood of prolonged pregnancy in nulliparous women. However, there is no association between cervical length at 20 to 24 weeks and the occurrence of prolonged pregnancy.

Fig. 1

Receiver operating characteristic curve analysis for sonographically measured cervical length at 37 weeks in predicting prolonged pregnancy. Number next to solid dot represents cervical length (mm) at 37 weeks (area under the curve 0.702, SE 0.060, p<0.005).

Fig. 2

Sonographically measured cervical length at 37 weeks and gestational age at delivery. There was a significant positive correlation between sonographically measured cervical length at 37 weeks and gestational age at delivery (r=0.387, p<0.0001).