Comparison of transabdominal and transvaginal ultrasonography for the assessment of cervical length at 16-23 weeks of gestation

The aim of this study was to assess the relationship between transabdominal and transvaginal ultrasonography for the cervical length assessment and to evaluate the predictive value of the transabdominal ultrasonography cervical length assessment for predicting preterm birth. A prospective cohort study was conducted. Transabdominal and transvaginal ultrasonography cervical length assessments were performed in 160 pregnant women between 16 and 23(+6) weeks of gestation. Transabdominal ultrasonography cervical length assessment was positively correlated with the transvaginal ultrasonography cervical length assessment. Mean +/- standard deviation of the cervical length was significantly different between transabdominal and transvaginal ultrasonography (36.4 +/- 5.4 vs. 41.2 +/- 5.4mm, p<.001). Transabdominal cervical length was shorter than the transvaginal cervical length with a mean difference of 4.8mm. The sensitivity, specificity, positive predictive value and negative predictive value for predicting preterm birth when the transabdominal cervical length was 35mm, were 50%, 52.1%, 9.1%, and 91.6%, respectively. In conclusion, transabdominal ultrasonography cervical length assessment is positively correlated with the transvaginal ultrasonography cervical length assessment. Transabdominal cervical length assessment was not a good predictor of preterm birth.