Hydrops fetalis is abnormal swelling in the body of a developing baby or newborn.
Hydrops fetalis can be immune-related (usually caused by Rh sensitization of the mother) or non-immune (caused by chromosomal abnormalities in the developing baby, anatomic abnormalities of the fetal heart, fetal anemia, infections, or other factors). Sometimes hydrops fetalis can be treated if it occurs in the second or third trimester. Left untreated, it may cause stillbirth or neonatal infant death.

