Hydrops fetalis is a serious condition in which abnormal amounts of fluid build up in two or more body areas of a fetus or newborn.

See also: Erythroblastosis fetalis

There are two types of hydrops fetalis: Immune and nonimmune. The exact cause depends on which form a baby has.

• Immune hydrops fetalis is a complication of a severe form of Rh incompatibility. Rh compatibility causes massive red blood cell destruction, which leads to several problems, including total body swelling. Severe swelling can interfere with how the body organs work.
• Nonimmune hydrops fetalis occurs when a disease or medical condition disrupts the body's ability to manage fluid. There are three main causes for this type: heart or lung problems, severe anemia (thalassemia), and genetic defects, including Turner syndrome.

The number of babies who develop immune hydrops fetalis has dramatically decreased since the introduction of the medicine RhoGAM, which is used to treat pregnant mothers at risk for Rh incompatibility.