Objective: To determine whether cord insertion can be consistently visualized and whether velamentous cord insertion and vasa previa can be consistently identified with color Doppler imaging during routine sonography in the mid-trimester.
Design: A prospective study.
Subjects: A total of 587 fetuses at 18-20 weeks' gestation.
Methods: During routine ultrasound examinations, the sonographer was instructed to take additional time and to image the placental cord insertion with color Doppler imaging and classify this as normal, velamentous or 'not seen'. When the insertion was velamentous, the sonographer was instructed to indicate whether or not it was vasa previa. The sonogram obtained at 18-20 weeks' gestation was used for comparison with outcome data.
Results: Cord insertion was visualized by color Doppler imaging in 99.8% (586/587) of the fetuses in our study. The mean time required for examination was 20 s and, in 95% of the cases, cord insertion was visualized within 1 min. The sonographic identification of velamentous cord insertion had a sensitivity of 100% (5/5), a specificity of 99.8% (580/581), a positive predictive value of 83% (5/6) and a negative predictive value of 100% (580/580). In our study, vasa previa was diagnosed at 18 gestational weeks in two cases and, in one of the cases, vasa previa was confirmed at delivery.
Conclusions: We could consistently identify cord insertion and velamentous cord insertion with color Doppler imaging during routine sonography in the mid-trimester. Transvaginal color Doppler imaging and serial scans were needed to identify vasa previa.