During pregnancy, the pregnant woman's blood group is checked, and a blood test is carried out to look for antibodies. If the woman is RhD negative and the baby is RhD positive, there is a blood group difference that can sometimes affect the baby's health.

Blood tests and preventive treatment can help reduce the risk of complications.

What is Rhesus D incompatibility?

Rhesus D (RhD) is a protein found on the surface of red blood cells. People are either RhD positive or RhD negative.

If a pregnant woman is RhD negative and the baby is RhD positive, her immune system may produce antibodies against the baby's red blood cells. This is known as RhD sensitisation.

These antibodies can affect the baby, particularly in future pregnancies. This is why identifying RhD incompatibility and preventing sensitisation are important.

How is RhD monitored during pregnancy?

Early in pregnancy

• All pregnant women have a blood test to determine their blood group and check for red blood cell antibodies.

At 25 weeks

• RhD-negative women have a blood test to check for red blood cell antibodies and determine the baby's RhD blood group using a sample of the mother's blood.

At 28 weeks

• RhD-negative women carrying an RhD-positive baby are offered an anti-D immunoglobulin injection to prevent sensitisation. If the baby is RhD negative, the injection is not needed.

After birth

• The baby's blood group is confirmed using a blood sample from the umbilical cord. If the mother is RhD negative and the baby is RhD positive, another anti-D injection is given, provided the mother has not already developed anti-D antibodies.

What does the anti-D injection do?

The injection contains anti-D antibodies that reduce the chance of the mother's immune system producing its own antibodies against RhD-positive red blood cells.

This preventive treatment helps protect both the current pregnancy and future pregnancies.