Article révisé par les pairs
Résumé : The placenta extrachorialis is an anatomic anomaly characterized by a transition of membranous to villous chorion at a distance from the placental edge, which is often poorly interpreted. Two forms can be distinguished: the placenta circummarginata, which is practically asymptomatic, and the placenta circumvallata, which is often associated with premature delivery and vaginal bleeding during pregnancy. Sonographic features of two circumvallate placentas with a morphological correlation are presented.