Placenta previa: avoiding false-negative diagnoses.

A retrospective analysis of 102 patients with clinically suspected placenta previa revealed that ten women (10%) were correctly diagnosed as having placenta previa, while two women (2%) had false-positive diagnoses. Three of the ten women who were correctly diagnosed as having placenta previa had scans that could easily have been misinterpreted as normal. Because a false-negative diagnosis of placenta previa is clinically much more serious than a false-positive diagnosis, these cases are elaborated upon. Recognition of a laterally positioned placenta previa and observation of blood in the region of the internal cervical os should minimize false-negative diagnostic errors.