What is hydrops fetalis characterized by?

Hydrops fetalis is characterized by the accumulation of fluid in at least two extravascular compartments within the fetus. This condition typically manifests as ascites (fluid in the abdominal cavity), pleural effusion (fluid in the lungs), and/or peripheral edema. The presence of fluid in multiple compartments indicates a systemic issue, which can be caused by a variety of underlying conditions, such as cardiac defects, anemia, infection, or chromosomal abnormalities.

In contrast, fluid accumulation in a single compartment would not meet the criteria for hydrops fetalis, as the diagnosis requires involvement of multiple areas. While heart defects may be a contributing factor to hydrops, they are not a defining characteristic of the condition itself. Additionally, increased placental thickness may occur in cases of hydrops and could be a sign of the underlying problem, but it is not a criterion for the diagnosis of hydrops fetalis. Therefore, fluid buildup in at least two extravascular compartments is the key defining feature.