Rh Hemolytic Disease

Excerpt

The Rhesus factor (Rh factor) is a surface antigen of erythrocytes. The term "Rhesus" was coined when discovered in Rhesus monkeys. The Rh blood group system consists of multiple antigens (over 50), but D, C, c, E, and e are the most common antigens identified. D antigen is mainly responsible for Rh disease due to its high immunogenicity. A person can be Rh-positive or Rh-negative based on the presence or absence of D antigen on the surface of red blood cells respectively.

Rh-hemolytic disease, also known as Rh incompatibility, is a condition that occurs when a woman with Rhesus-negative blood type is exposed to Rhesus-positive blood cells, leading to the development of anti-D antibodies by a process called isoimmunization. After this sensitization, these maternal alloantibodies (IgG immunoglobulins) may persist for life and move freely across the placenta to the fetal circulation during subsequent pregnancies, where they lead to the destruction of fetal erythrocytes after forming antigen-antibody complexes with their surface D antigen. This results in alloimmune hemolytic anemia in the fetus, known as erythroblastosis fetalis. The severity of illness depends greatly on the number of immunoglobulins, the gestational age, and the enzymatic activity of the fetus.

If undiagnosed, the mortality rate is high, at 24% in neonates. Universal parental Rh screening and prophylaxis treatment with Rh immunoglobulin have significantly reduced neonatal mortality rates.