I was told I had ‘rhesus negative’ blood when I went for my pregnancy screening. What does this mean?
At your first antenatal appointment you are likely to be offered several blood tests. One of the tests is to find out your blood group. Your blood may be in one of four groups: A, B, AB or O.
The blood will also be either rhesus positive or rhesus negative. People whose blood is rhesus positive have a substance known as D antigen on the surface of their red blood cells. Rhesus negative people do not. About 15% of women are rhesus negative. This isn't usually a concern for a first pregnancy, but it may mean some extra care is needed to avoid problems if you get pregnant again.
Does my baby have the same type of blood as I do?
A rhesus negative woman can be pregnant with a rhesus positive baby if the baby's father is rhesus positive. If any of the baby’s blood enters the woman’s bloodstream, the woman’s immune system can develop antibodies (infection-fighting proteins) against the rhesus antigens. This is known as sensitisation. A transfer of blood can occur during birth, or if the woman has a bleed or an injury.
Risks of rhesus negative blood
Production of the antibodies is not a problem in a first pregnancy, but when the woman is pregnant next time with a rhesus positive baby, her antibodies can attack that baby’s red blood cells. This can result in a serious condition called haemolytic disease of the newborn, which leads to anaemia and jaundice in the baby.
If the woman is given an injection of a solution called ‘Anti-D’, it will ‘mop up’ any rhesus positive antigens, preventing production of antibodies against the baby. Anti-D injections reduce the risk of a rhesus negative woman becoming sensitised.
NICE recommends routine antenatal administration of Anti-D to all rhesus negative women in case sensitisation occurs. This can be given as a one-off dose at 28-30 weeks or as two doses at 28 and 34 weeks. It is quite safe for both the mother and the baby.