Chorioamniotic separation

Chorioamniotic separation (CAS) is an intra-uterine event which can occur in pregnancy and is characterised by separation of placental (chorion) and fetal (amnion) membranes.

The membranes are separated in early gestation, accounting for the appearance of the amniotic sac. After approximately 14 weeks gestation, these membranes fuse and are indistinguishable as seperate entities. Rarely, a chorioamniotic separation can occur later in gestation. It can be focal or extensive, with the amniotic membrane becoming either free floating or adherent to the fetus.

Causes

Most reported cases occur after invasive intra-uterine procedures such as:

Some cases occur spontaneously which is then termed a primary chorioamniotic separation.

Associations
  • increased rates of underlying fetal chromosomal and developmental abnormalities have been associated with sporadic cases 5
Antenatal ultrasound

A chorioamniotic separation is usually sonographically detected as a visible free-floating or adherent membrane surrounding the fetus. The separation can extend throughout the entire uterine cavity and over the surface of the placenta.

Sonographic detection of a small chorioamniotic membrane separation especially before 14 weeks gestation is considered a benign incidental finding 5,7

Knowledge of potential complications is however useful. A careful search for aneupliodic and other developmental anomalies is often recommended if a spontaneous chorioamniotic separation is detected after 14 weeks.

Recognised complications following a large separation include 4:

Considerations for ultrasound appearances include:

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Article Information

rID: 13400
System: Obstetrics
Tag: cases
Synonyms or Alternate Spellings:
  • Chorioamniotic membrane separation (CMS)
  • Chorioamniotic separation (CAS)
  • Chorio-amniotic separation (CAS)
  • Chorio-amniotic separation
  • Chorioamniotic membrane separation
  • Chorio-amniotic membrane separation (CMS)
  • Chorio-amniotic membrane separation

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