Antenatal diagnosis of placenta accreta: a review.

The incidence of placenta accreta should rise steadily over the next century as the frequency of Cesarean sections and advanced maternal age, both independent risk factors, increases. Patients who are at risk should be identified before an ultrasound examination and the characteristic findings searched for. In the first trimester, these include a low-lying sac that appears to be attached to the anterior wall of the uterus. As early as 16 weeks irregular vascular sinuses appear, which have turbulent flow within. The bladder wall may appear interrupted or have small bulges of the placenta into the bladder space. Absence of the normal echolucent space between the placenta and myometrium is not a reliable sign by itself, since this space may be absent in normal patients with an anterior placenta. Color Doppler will show that some of the placental sinuses traverse the uterine wall. Magnetic resonance imaging has not yet been shown to aid in the diagnosis, but in the future, with improvement of resolution and shortened sequences, it should be particularly useful in identifying the patients that have placenta percreta.