Antibodies are produced by the immune system in response to foreign cells. Most people know of antibodies in relation to infection – the lifelong immunity one gets after a measles infection, for example, is because your body produces antibodies to the measles virus. During pregnancy, antibodies usually refer to the woman’s blood group, in a condition called alloimmunisation.
Babies inherit their blood group from both their mother and father – therefore the baby’s blood group is not identical to the mother’s. Occasionally, there can be an incompatibility between the baby’s blood group and that of the mother – the mother’s body sees her baby’s red blood cells as “foreign” and forms antibodies to fight the baby’s red blood cells (alloimmunisation). Once a woman forms antibodies in her blood they remain there for life, with the potential to affect all subsequent pregnancies.
The antibodies can cross the placenta and attack the baby’s red blood cells, causing fetal anaemia. The overall risk of this is low and is determined by the type and quantity of antibody in the mum’s blood. Women who have had an affected baby in a previous pregnancy are at especially high risk. The most common type of antibody is called “D” (hence susceptible women are given “anti-D” during pregnancy). Less common antibodies involved in this process include “Kell” and “c”, with a long list of even rarer ones. At SHORE FOR WOMEN, we have huge experience in caring for alloimmunised pregnancies, both the common “Rh-D” alloimmunisation, as well as rarer antibodies.
All pregnant women have an antibody blood test at 10-12 weeks and again at 28 weeks. Women with antibodies should have a repeat blood test monthly until 28 weeks and every 2 weeks there after. If the antibodies are very high, regular specialised ultrasound scans are recommended. Your SHORE FOR WOMEN fetal medicine specialist will discuss this with you and we can perform the specialised scans.
In most cases, alloimmunisation has no major impact on your labour and delivery. Because babies of women with these antibodies are more likely to be jaundiced, sometimes it is reasonable to consider induction of labour after 37 weeks is reached. Rarely, alloimmunisation can be associated with severe fetal anaemia. In rare cases, babies require a blood transfusion(s) during the pregnancy to treat the anaemia. In these severe cases, delivery before 37 weeks may be necessary. Dr. Colin Walsh has recently published 2 leading studies on alloimmunised pregnancies.