Chorioamniotic separation is an intrauterine event that can occur in pregnancy and is characterized by separation of the placental (chorion) and fetal (amnion) membranes.
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Epidemiology
Associations
increased rates of underlying fetal chromosomal and developmental abnormalities have been associated with sporadic cases 5
Pathology
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 separate 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.
Etiology
Most reported cases occur after invasive intrauterine procedures such as:
previous amniocentesis: small degrees of chorioamniotic separation are frequently present after amniocentesis
Some cases occur spontaneously which is then termed "primary chorioamniotic separation".
Radiographic features
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 up to the base of the umbilical cord and over the surface of the placenta.
Sonographic detection of a small chorioamniotic separation before 14 weeks gestation is a normal and benign incidental finding 5,7. A careful search for aneuploidy and other developmental anomalies is recommended if a spontaneous chorioamniotic separation is detected after 14 weeks.
Treatment and prognosis
Complications
Recognized complications following a large separation include 4:
umbilical cord complications
amniotic band formation
Differential diagnosis
Considerations for ultrasound appearances include:
amniotic band going through the periphery: can be also a complication of chorioamniotic separation
subchorionic hemorrhage dissecting around the endometrial cavity 2