If the fetus is RH positive and the carrying mother is Rh-negative, fetal blood cells are destructed in case the RhoGAM injection is not given. Why in the first place does fluid accumulate in the fetal body as a result of the reaction?
Hydrops fetalis is a complication of Hemolytic Disease of Newborn (HDN). This happens during pregnancy when the mother is Rh negative but the baby is Rh positive. When Rhogam or Rh immune globulin is not injected, red blood cells are destroyed or hemolyzed as they are being attacked by the mother's antibodies. Anemia is the body's response to hemolysis. When organs of the baby can no longer handle the anemia, the body tries to make more red blood cells in the bone marrow, liver and spleen at an accelerated rate. This triggers the organs to get bigger. It causes severe swelling then as a result, the heart will start to fail. This causes the accumulation of large amounts of fluid build up in the baby's tissues and organs.