Rhesus disease is a condition where antibodies in a pregnant woman’s blood destroy her baby's blood cells.
The condition is also known as haemolytic disease of the foetus and newborn.
Rhesus disease only happens when the mother has rhesus-negative blood (RhD negative) and the baby in her womb has rhesus-positive blood (RhD positive). The mother must have also been previously sensitised to RhD-positive blood.
Sensitisation happens when a woman with RhD negative blood is exposed to RhD positive blood, usually during a pregnancy with an RhD positive baby. The woman’s body responds to the RhD positive blood by producing antibodies (infection-fighting molecules) that recognise the foreign blood cells and destroy them.
If sensitisation occurs, the next time the woman is exposed to RhD positive blood her body will produce antibodies immediately. If she is pregnant with an RhD-positive baby, the antibodies can cross the placenta, causing rhesus disease in the unborn baby. The antibodies can continue attacking the baby's red blood cells for a few months after birth.
Rhesus disease does not harm the mother, but it can cause the baby to become anaemic and develop jaundice (yellowing of the skin and whites of the eyes).
Read more about the causes of rhesus disease and the symptoms of rhesus disease.
Preventing rhesus disease
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. If the mother is RhD negative, she will be offered injections of anti-D immunoglobulin at certain points in her pregnancy when she may be exposed to the baby’s red blood cells. This anti-D immunoglobulin helps to remove the RhD foetal blood cells before they can cause sensitisation.
If a woman has developed anti-D antibodies in a previous pregnancy (she is already sensitised) then these immunoglobulin injections do not help. The pregnancy will be monitored more closely than usual, as will the baby after delivery.
Read more about preventing rhesus disease and diagnosing rhesus disease.
Treating rhesus disease
If an unborn baby does develop rhesus disease, the treatment will depend on how severe it is. A blood transfusion to the unborn baby may be needed in more severe cases. After delivery, the child is likely to be admitted to a neonatal unit (a hospital unit that specialises in caring for newborn babies).
Treatment for rhesus disease after delivery 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 (when a baby dies in the womb before it is born). In other cases, it could lead to brain damage, learning difficulties, deafness and blindness. However, treatment is usually effective and these problems are uncommon these days.
Read more about treating rhesus disease and the complications of rhesus disease.