What type of hydrops occurs due to the mother's immune reaction against the fetus?

Immune hydrops is a condition that specifically arises from the mother’s immune response toward the fetus. This occurs when there is an incompatibility between maternal and fetal blood types, most commonly seen with Rh incompatibility. In this scenario, the mother's immune system produces antibodies against the fetal red blood cells, leading to their destruction (hemolysis). This hemolytic process results in anemia in the fetus, and as a compensatory mechanism, the fetal heart works harder to maintain adequate circulation. The increased workload can lead to heart failure and fluid accumulation in various body compartments, resulting in hydrops fetalis.

The specific mechanism involves immunoglobulin G (IgG) antibodies crossing the placenta, targeting the fetal blood, which ultimately causes the clinical presentation of immune hydrops. This distinguishes it from other forms of hydrops, which may have different etiologies such as non-immune causes like cardiac defects or infections that lead to similar fluid accumulation but through different pathophysiological mechanisms. Understanding this distinction is important for proper management and intervention in affected pregnancies.