Rh Incompatibility

Rh incompatibility arises when a pregnant woman lacks the Rh (D) antigen on her red blood cells (Rh-negative) while the fetus inherits it from an Rh-positive father. During pregnancy or delivery, fetal blood may enter the maternal circulation, triggering the mother's immune response to produce anti-Rh antibodies. These IgG antibodies can cross the placenta in subsequent pregnancies, destroying fetal RBCs and causing hemolytic disease of the fetus and newborn (HDFN).

Mechanism and Risk

Sensitization often happens via minor fetal-maternal hemorrhage from trauma, miscarriage, or procedures like amniocentesis. First pregnancies are usually unaffected as antibodies form late, but risks escalate in later Rh-positive pregnancies. Without intervention, it leads to fetal anemia, jaundice, hydrops fetalis, or stillbirth.

Prevention

RhoGAM (Rh immunoglobulin) injections at 28 weeks of gestation and postpartum neutralize fetal Rh antigens, preventing antibody formation in 99% of cases. Non-invasive prenatal testing monitors fetal Rh status early.

Diagnosis and Treatment

Maternal antibody titers, ultrasound for fetal anemia, and Doppler middle cerebral artery velocity aid diagnosis. Severe cases require intrauterine transfusions; newborns receive phototherapy, IVIG, or exchange transfusion for hyperbilirubinemia.