Rhesus isoimmunisation

What it is

Rh incompatibility is autosomal recessive. An event that lets fetal blood into an Rh-negative mother sensitizes her, and from then on the pregnancy is at risk: fetal anemia before birth, hemolytic disease of the newborn after it. The one line to hold on to: anti-D immunoglobulin is used prophylactically to prevent Rh sensitization in Rh-negative women, not as a treatment for those who are already sensitized. After sensitization there is no longer a sensitization to prevent. Around 15% of mothers are rhesus negative, and the D antigen is the most important antigen of the rhesus system, which itself stands with the ABO system as the most important antigen found on red blood cells. If a rhesus negative mother delivers a rhesus positive child a leak of fetal red blood cells may occur, anti-D IgG antibodies form in the mother, and in later pregnancies these cross the placenta and cause haemolysis in the fetus; this can also happen in the first pregnancy because of leaks.