Vaginal ultrasound for diagnosis of placenta previa.

Transvaginal sonography was compared with transabdominal sonography in 35 women with suspected placenta previa. The transvaginal sonographic technique did not result in vaginal bleeding in any of the patients. The internal os and its relationship to the location of the placenta were visualized by transvaginal sonography in all patients, but only in 24 patients (69%) by transabdominal sonography. Transvaginal sonography ruled out placenta previa in 13 cases thought to be placenta previa by abdominal sonography. The transvaginal diagnosis in these 13 patients was confirmed at delivery. Thirty-four of the 35 women have been delivered. The diagnosis at delivery confirmed the transvaginal sonographic diagnosis in 29/34 cases and the transabdominal diagnosis in 16/34. Transvaginal sonography did not predict the delivery diagnosis in five patients who were erroneously believed to have placenta previa by both sonographic techniques.