Circumvallate placenta

Circumvallate placenta refers to a variation in placental morphology in which, as a result of a small chorionic plate, the amnion and chorion fetal membranes ‘double back’ around the edge of the placenta.

The prevalance is estimated to be at around 1-7% 3.

There is inward insertion of membranes from the edge towards the center of the placenta (from deep implantation of the placenta into the decidua). Because of this excessive implantation, the placenta covers more than half of the fetal sac. The placenta reduces this excessive covering to the normal one-fourth by separating from the uterine wall, with the resultant back folding of the placenta and fetal membranes towards the chorionic surface.

This can be accompanied by tethering of membranes, frequently often in association with a marginal infarction, haemorrhage, or fibrin deposition. 

Antenatal ultrasound

May show a peripheral rim of chorionic tissue appearing as an echodense ridge (placental shelf2,6.

On 3D ultrasound, it has an appearance similar to a tire (the "tire sign").

Recognised complications include 1,4:

For a raised placental edge on ultrasound:

Ultrasound - obstetric
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Article information

rID: 9563
System: Obstetrics
Synonyms or Alternate Spellings:
  • Placenta extrachorialis

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Cases and figures

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    Figure 1: diagram - circumvallate placenta
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