Diagnosis of placenta previa by ultrasonography: a review at Ramathibodi Hospital.

From 1,000 ultrasonographic examinations reviewed there were 80 (8%) done for the exclusion of placenta previa. Only 83.6 per cent of these had complete medical records and were the subjects of this study. The most common reason for requesting ultrasonography was antepartum hemorrhage (79.1%). False-positive and false-negative of the report were 16.7 per cent and at least 4.2 per cent respectively. Based on the theory of placental migration it can be recommended that a minor degree of placenta previa diagnosed in the early stage of pregnancy does not need follow-up scanning while the diagnosis of placenta previa totalis follow-up scanning is imperative. A judicious decision in the combined usage of ultrasonography and double-set-up technique can reduce the risk of brisk bleeding and unnecessary cesarean section.