Non-immune hydrops can also be unrelated to anemia, for example if a fetal tumor or congenital pulmonary airway malformation increases the demand for blood flow.

Rh disease develops in the event of a second pregnancy where the mother's immune system launches an attack, via IgG, against the infant's Rh-D positive blood cells.

Rh disease can be prevented by administration of anti-D IgG (Rho(D) Immune Globulin) injections to RhD-negative mothers during pregnancy and/or within 72 hours of the delivery.

However, a small percentage of pregnant mothers are still susceptible to Rh disease even after receiving anti-D IgG (Rho(D) Immune Globulin).

The excessive pumping of blood causes the left side of the heart to fail leading to pulmonary edema.

The coupled vasoconstriction and pulmonary hypertension causes the right side of the heart to fail which in turn, increases the venous hydrostatic pressure in the body.

Prenatal ultrasound scanning enables early recognition of hydrops fetalis and has been enhanced with the introduction of MCA Doppler.