Cervical length measurements in pregnancy are longer when measured with three-dimensional transvaginal ultrasound

Abstract

Objective: To compare cervical length measurements obtained by transvaginal two-dimensional (2D) and transvaginal three-dimensional (3D) ultrasound. Study design: Thirty-four consecutive women having transvaginal assessment of cervical length as part of an obstetric ultrasound examination consented to have a 3D ultrasound scan. The cervical lengths obtained by the two methods were compared by Student's t test and regression equations. Results: The mean cervical 2D length was 35.7 ± 1.4 (SE) mm and 3D length was 43.7 ± 1.9 mm (difference 8.0 mm ± 0.98, p < 0.001). In the 12 women with cervical length on 2D < 35 mm, there was a 7.5 ± 1.7 (SE) mm difference (p = 0.007). In all but one woman the 3D length obtained was the same or longer than the 2D length. The longer the cervical length on 3D imaging, the greater the difference from the 2D length (p < 0.001). Conclusion: The longer 3D cervical measurements may reflect the inability to measure the cervix adequately with 2D imaging, owing to anatomical factors. This finding may be useful in improving the predictive value of transvaginal ultrasound in assessing the risk for preterm delivery.