Rhesus disease

Rhesus disease - also known as haemolytic disease of the newborn - is a condition where antibodies in a pregnant woman’s blood attack her baby's blood cells. This can only happen if the following three criteria have been met:

• the mother has rhesus-negative blood (RhD negative),
• the baby has rhesus-positive blood (RhD positive), and
• the mother has previously been sensitised to RhD positive blood.

Sensitisation

Sensitisation occurs when a woman with RhD negative blood is exposed to RhD positive blood. This could happen during a pregnancy with a 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 preparing to attack it with antibodies (infection-fighting chemicals). The first time this happens it is known as sensitisation.

If sensitisation has occurred, the next time the woman is exposed to RhD positive blood, her body will start to produce antibodies immediately. If she is pregnant with a RhD positive baby, the antibodies can cross the placenta and cause rhesus disease in the baby.

See the causes section for more information about sensitisation.

How common is rhesus disease?

Nowadays, rhesus disease is uncommon because the condition can be easily prevented.

An injection of anti-D immunoglobulin was introduced in 1977 to prevent sensitisation, and has reduced the number of cases of rhesus disease by 90% since being introduced.

The injection is given to RhD negative women who may have been sensitised to RhD positive blood during pregnancy. It prevents the woman developing the antibodies that attack the baby’s blood.

Outlook

The symptoms of rhesus disease in newborn babies include jaundice and anaemia (a lack of red blood cells). Babies with the condition will usually need to be admitted to a neonatal unit (a hospital unit that specialises in caring for newborn babies). Treatment includes phototherapy (treatment with light) and, possibly, blood transfusions.

If rhesus disease is left untreated, the effects of the jaundice in the newborn baby can lead to learning difficulties, deafness, and blindness. Severe cases can lead to stillbirth (when a baby dies in the womb before it is born).