The antenatal diagnosis of placental attachment disorders.

PURPOSE OF REVIEW: The incidence of placenta accreta is increasing as the number of cesarean sections increases. Separation of the placenta from the uterus in this situation may result in torrential bleeding. Antenatal diagnosis allows modification of the approach to delivery to conserve blood loss and avoid major medical problems.

RECENT FINDINGS: Most of the imaging literature confines itself to patients who are at risk due to previous surgery and a placenta previa. In these patients, the most reliable sign of placenta accreta is the presence of irregular vascular spaces with arterial flow. In almost all patients, the signs needed for the diagnosis are present at the time of the screening examination at 18 weeks. Ultrasound is quite accurate in predicting severe placenta accreta in at-risk patients. Less severe cases, in which the placenta is solely difficult to separate, may not have any ultrasound findings. Nothing is known about the ultrasound appearance of placenta accreta in patients who have not had previous uterine surgery.

SUMMARY: Antenatal identification of placenta accreta is possible with high sensitivity in patients with placenta previa and a previous cesarean section.