Rhesus disease – also known as haemolytic disease of the foetus and newborn – is a condition where antibodies in a pregnant woman’s blood destroy her baby's blood cells.
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. This could happen during a pregnancy with an RhD-positive baby, or if the woman has a blood transfusion with RhD-positive blood.
The woman’s body responds to the RhD-positive blood by generating antibodies (infection-fighting protein molecules) that recognise the "alien" blood cells and destroy them. This is known as "sensitisation" the first time it happens.
If sensitisation has already occurred, the next time the woman is exposed to RhD-positive blood her body will start to produce antibodies immediately, and in larger amounts. If she is pregnant with an RhD-positive baby, the antibodies can cross the placenta and cause rhesus disease in the unborn baby. After the baby has been born, the mother's antibodies can remain in the baby for a few months and can continue to attack its red blood cells.
Find out what causes rhesus disease.
Preventing rhesus disease
Rhesus disease is uncommon these days, because the condition can usually be prevented.
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 then 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 the process of sensitisation.
If a woman has developed anti-D antibodies in a previous pregnancy (she has already become sensitised) then these immunoglobulin injections do not help. The pregnancy will be monitored much more closely than usual, as will the baby after delivery.
Read more about how rhesus disease is prevented.
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 includes phototherapy, blood transfusions and a solution of antibodies given through a vein to prevent red blood cells being destroyed (intravenous immunoglobulin).
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 learning difficulties, deafness, blindness and cerebral palsy.
Read more about the complications of rhesus disease.
