Anti-S Antibody: A Rare Cause of Fetal Hydrops in a Previously Sensitized Mother

Anti-S is an IgG antibody and a rare cause of hemolytic disease of the fetus and newborn. A 38 year old woman with blood group O Rh-positive presented to the hospital at 30 weeks gestation. Her past medical history was significant for sickle cell disease and alloantibodies against the Fya, Jkb, and S antigens. Obstetric ultrasound showed the fetus to have developed scalp edema, cardiomegaly, small pericardial effusion, and large ascites. Periumbilical blood sampling results showed the fetus blood type as blood group O Rh-positive with anti-S and hemoglobin of 2 gm/dL. After multiple intrauterine transfusions of red blood cells, the fetal hemoglobin increased to 12.9 g/dL. Anti-S can cause fetal hydrops, although it is rare. All pregnant women with anti-S should be closely monitored and treated during pregnancy for the possibility of developing a severe hemolytic disease of the fetus and newborn.