Diagnosis of placenta previa by transvaginal sonography.

The evolution of the sonographic diagnosis of placenta previa is reviewed with special emphasis on transvaginal sonography (TVS), which has been proved accurate at diagnosing different degrees of placenta previa, such as complete, partial, marginal and low-lying. Bleeding tendency and the need for Caesarean delivery increases when the placental edge is within 3 cm of the internal os. There is no association between bleeding and use of transvaginal probes. The early diagnosis of addition abnormalities of implantation (e.g. placenta accreta) using transvaginal colour flow Doppler widens the prospects for carefully planned patient management. In conclusion, TVS should be the principal diagnostic modality used in the work-up of an obstetric patient with vaginal bleeding. The ease of performance and the clarity and accuracy of method and the additional information about implantation that it can provide will soon make TVS the 'golden standard' in the diagnostic process of placenta previa.