The condition resulting from destruction (haemolysis) of the red blood cells of the fetus by antibodies in the mother’s blood passing through the placenta. When an exchange occurs between fetal and maternal blood (as at delivery, placental abruption, threatened miscarriage, or invasive procedures), the passage of red cells into the maternal circulation provokes an antibody response to the fetal red blood cell antigen in the mother. This most commonly happens when the red blood cells of the fetus are Rh positive (i.e. they have the rhesus factor) but the mother’s red cells are Rh negative. For the rhesus antigen, the primary IgM antibodies (see immunoglobulin) do not cross the placenta, but if the mother is exposed in another pregnancy, IgG antibodies do cross the placenta. This may result in very severe anaemia of the fetus, leading to heart failure with oedema (hydrops fetalis) or stillbirth. When the anaemia is less severe the fetus may reach term in good condition, but the accumulation of the bile pigment bilirubin from the destroyed cells causes severe jaundice after birth, which may require exchange transfusion. If untreated, it may cause serious brain damage (see kernicterus). Other red cell antibodies that are clearly associated with fetal anaemia are D, Kell, and c.
A blood test early in pregnancy enables the detection of antibodies in the mother’s blood and the adoption of various precautions for the infant’s safety, including Doppler measurement of the fetal cerebral vessels (MCA Doppler; see Doppler ultrasound) to detect fetal anaemia, which may require intrauterine transfusion. The incidence of the disease has been greatly reduced by preventing the formation of antibodies in a Rh-negative mother (see anti-D immunoglobulin).
Subjects: Medicine and Health.