Pregnant mothers produce IgG red cell antibodies, which can cross the placenta and destroy the baby’s red cells, causing haemolytic disease of the newborn (HDN).
The antibodies that cause HDN are directed against antigens on the baby's red cells that are inherited from the father and are absent in the mother.
The mother may develop these antibodies if fetal red blood cells cross the placenta (fetomaternal haemorrhage) during pregnancy or delivery. They may also result from a previous red cell transfusion.
Antibody to the Rh(D) antigen is the most frequent cause of HDN. IgG antibodies against other Rh antigens (including c, e, C, E) and blood group antigens (including Fya and K) occur in about 0.5% of pregnancies.
In the most severe cases of HDN, the fetus may die in utero or be born with severe anaemia that requires replacement of red cells by exchange transfusion.
It is interesting to note that anti-Kell (anti-K) antibody produces anaemia in the neonate by suppressing marrow erythroid activity, rather than by increased haemolysis of fetal red cells.(1)
There may also be severe neurological damage after birth as a result of a high bilirubin level (kernicterus).
Effective care during the affected pregnancy and of the newborn require the skills of a specialist team.
Although ABO incompatibility between mother and fetus is common, severe HDN due to IgG anti-A and anti-B antibodies is very rare.
The ABO and Rh(D) group of all pregnant women should be determined when they first attend for antenatal care.
The mother's blood should also be tested for atypical IgG red cell antibodies, as these may also cause HDN.
Perform routine antenatal screening in accordance with the Guidelines for Blood Grouping & Antibody Screening in the Antenatal & Perinatal Setting(2) and the Royal Australian and New Zealand College of Obstetrics and Gynaecology (RANZCOG) College Statements(3).
Specialist teams should care for pregnancies that are potentially affected by HDN with facilities for early diagnosis, intrauterine transfusion and support of high dependency neonates.
► Read about Pregnancy and Anti-D, and Rh(D) Prophylaxis of pregnant women with Rh(D)-negative blood group and no pre-existing Anti-D antibodies
The referral should be made before 20 weeks in those women who have had a previously severely affected baby, unless there is a new partner who is negative for the relevant antigen.
If antibodies are detected, the levels should be monitored frequently throughout the pregnancy in case they increase in titre.
Rising levels are likely to be indicative of HDN developing in the fetus.
Amniocentesis and the level of bilirubin in the amniotic fluid will give a clearer guide to the severity of the disease.
Management of an affected fetus may include intrauterine transfusion, early delivery, phototherapy and exchange transfusion.
