The Ultrasound Diagnosis of Placenta Accreta

Abstract

Placental attachment disorders (placenta accreta, increta and percreta) have increased in the last 20 years as the number of Caesarean sections and maternal age have increased. Although maternal mortality has decreased in major centers, probably due to improvements in blood banking and intensive care, it is still a life threatening condition and requires advance planning and significant hospital resources. Placenta accreta can cause problems in any trimester, e.g. early uterine rupture, bleeding after dilatation and curettage and massive bleeding at delivery. For these reasons there have been active efforts to identify placenta accreta prospectively. In early pregnancy attachment of the gestational sac to a previous Caesarean section scar or unusual vascular spaces in the early placenta suggest placenta accreta. In the second and third trimesters the most useful sign is the presence of irregular vascular lacunae with arterial blood flow within them. Colour Doppler is an adjunct technique but grey scale ultrasound is adequate for most diagnoses. Although the literature has addressed the appearance of placenta accreta in patients who have placenta praevia and previous Caesarean sections, there is as yet no knowledge of the appearance in patients without previous surgery, an occurrence which is rare but does exist. The role of Magnetic Resonance Imaging is not yet clear, but with eventual improvement in scan times and resolution it may be used in the future in patients who have ultrasound evidence for accreta.