Prediction of risk for vasa previa at 9-13 weeks' gestation

Aim: To assess the usefulness for predicting vasa previa by detecting a cord insertion site in the lower third of the uterus between 9 and 13 weeks' gestation. Methods: The positional relationship between the uterine cavity and the cord insertion site was examined in consecutive subjects prospectively using ultrasonography at 9-13 weeks' gestation. The distance between the internal os and the fundus was divided equally into three parts. Cord insertions in the lower third were defined as cases; other insertions were defined as controls. Placental and umbilical cord abnormalities at the time of the delivery were analyzed between the two groups. Results: The cord insertion sites were identified as 139 (10.6%) cases with low cord insertion and 1172 control cases. The case subjects frequently had an abnormal placental form (6.5% vs 2.1%, RR 3.2, 95% CI 1.5-7.0) or placenta previa (4.7% vs 1.3%, RR 3.5, 95% CI 1.3-9.1). The frequencies of velamentous cord insertion were 7.2% in cases and 0.9% in controls (RR 8.1, 95% CI 3.4-19.6). Three cases (2.2%) of vasa previa were observed in the cases, but none were observed in the controls (P = 0.001). Placental abruption occurred in 4.3% of the cases and 0.9% of the controls (RR 4.7, 95% CI 1.7-13.1). Conclusion: Screening sonography in the late first or early second trimesters and following up at the second trimester in cases with low cord insertion is a useful way to detect vasa previa.