Nuclear placentography.

Localization of the placenta by radionuclide imaging techniques is useful in assessing the cause of vaginal bleeding late in pregnancy. Placenta previa is the most threatening cause of late gestational bleeding, and the acceptably high accuracy of nuclear placentography in detecting this condition is well-established. Nevertheless, B-mode ultrasonography is a preferable method because it delivers no ionizing radiation and is capable of identifying the cervix in virtually all patients. The latter method will eventually replace nuclear placentography.