Morphological abnormality of the placenta in which transition from a membranous to villous chorion does not occur at the placental edge but at some variable distance within the circumference of the placenta.
- Chorionic plate (fetal side) is smaller than the basal plate (maternal side)
Types:
There are 2 types of extrachorial placenta:
- Circummarginate placenta. Margin of chorionic plate appears as a raised, thin fibrous rim at the margin of the chorionic plate where the fetal vessels appear to terminate.
- Circumvallate placenta. Thickened membranous rim, composed of a double fold of amnion and chorion with degenerated decidua and fibrin in between, is folded inward towards the center.
Complications
- Intrauterine growth restriction (IUGR)
- Antepartum haemorrhage (APH)
- Retained placenta