A method for improving the accuracy of placental localization by ultrasound is offered. The simple adjustment of the far gain setting, without any other alteration in the procedure, gave 100% accuracy, with the correct diagnosis of all posterior placentas. Fifty-one randomly chosen gravid patients were scanned prior to a) aminiocentesis or b) cesarcan section, as part of a fetal growth curve study, and c) in every case of third trimester bleeding. All cases were correctly diagnosed, including 5 placenta previas and 25 posterior placentas. By diagnosing the cases with a posterior placenta, the most common cause of error was eliminated. Examples of the use of ultrasound for diagnosing the causes of antenatal bleeding are presented.

© 1973 The American College of Obstetricians and Gynecologists