Rhesus disease occurs during pregnancy when there is an incompatibility between the blood types of the mother and baby.
Everybody has one of 4 blood types (A, B, AB or O). You inherit your blood group from a mix of your parents' genes. These blood types are further identified as being either positive or negative. This shows your 'Rhesus factor' (RhD), which indicates if you have a protein known as 'D antigen' on the surface of your red blood cells.
Around 17 out of 100 people in Australia have a negative blood type. If your blood is RhD negative, it isn’t usually a problem, unless you are pregnant and your baby happens to be RhD positive. This can happen if the baby’s father is RhD positive.
The problem can occur if a small amount of the baby’s blood enters the mother’s bloodstream during pregnancy or birth, the mother can produce antibodies against the rhesus positive cells (known as ‘anti-D antibodies’). This is called a 'sensitising event'.
There are a number of ways that this can occur:
- some tests you may have during your pregnancy can be invasive, such as chorionic villus sampling (CVS) or amniocentesis
- vaginal bleeding
- miscarriage or termination
- abdominal trauma, such as, a blow to the abdomen
- if your baby is in a breech position and you have an external cephalic version
- during labour
A sensitising event usually doesn’t affect the first pregnancy, but if the woman has another pregnancy with a rhesus positive baby, her immune response will be greater and she may produce a lot more antibodies. These antibodies can cross the placenta and destroy the baby’s blood cells, leading to a condition called 'rhesus disease', or 'haemolytic disease of the newborn'. This can lead to anaemia, jaundice and brain damage in the baby.
Rhesus disease is uncommon these days because it can usually be prevented using injections of a medication called 'anti-D immunoglobulin'. All women are offered blood tests as part of their antenatal screening to determine whether their blood is RhD negative or positive.
The injection is offered at to rhesus negative women who have rhesus positive partners at 28 and 34 weeks of pregnancy. It can also be given at anytime if there is concern a sensitising event has happened. You can also have the injection after the baby has been born and tests confirm your baby is RhD positive. The only way to find out if a baby is RhD positive is after they are born and the umbilical blood can be tested.
The anti-D injection is safe for both the mother and the baby.
If a woman has developed anti-D antibodies in a previous pregnancy (she's already sensitised) then these immunoglobulin injections don't help. The pregnancy will be monitored more closely than usual, as will the baby after birth.
If an unborn baby does develop rhesus disease, treatment depends on how severe it is. A blood transfusion to the unborn baby may be needed in more severe cases. After birth, the child is likely to be admitted to a neonatal intensive care unit (a hospital unit that specialises in caring for newborn babies).
Treatment for rhesus disease after birth can include a light treatment called phototherapy, blood transfusions, and an injection of a solution of antibodies (intravenous immunoglobulin) to prevent red blood cells being destroyed.
If rhesus disease is left untreated, severe cases can lead to stillbirth. In other cases, it could lead to brain damage, learning difficulties, deafness and blindness. However, treatment is usually effective and these problems are uncommon.
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Last reviewed: May 2020