·Acardia- Acardia occurs in 1% of monozygote twin pregnancies. The pregnancy in which this anomaly occurs will have a single chorion and a single placenta, but there may be one or two amnions. When a monochorionic twin pregnancy has only one amnion, acardia risk is six times as great as when two amnions are present. US reveals absent cardiac motion in the abnormal twin.
Types of Acardia
·Acardius acephalus- This is the most common type of acardia (60—75%). There is no head. The abdomen is developed but there are no thoracic organs. The upper extremities may or may not be present. PH may be present with functioning kidneys.
·Acardius anceps- The head and face are partially developed. The body and extremities are developed but the heart is absent. There is increased amount of soft tissue with or without cystic areas. PH may be present if the fetus has functioning non-obstructed kidneys.
·Acardius amorphus- A formless blob containing all tissue types but no recognizable organs. This differs from a teratoma only in its attachment to an umbilical cord.
·Acardius acormus- There is a head but no body. This is the rarest type.