Can your blood group harm your unborn baby?
What Rhesus Negative Blood means in pregnancy
By Justine Swann BSc
Around 15% of the population has a Rhesus Negative blood group.
Is it a problem to be rhesus negative and pregnant? Well, yes, it can be if it’s not managed correctly.
Your inherited genes determine your blood type, and your baby’s blood may be different to yours.
At the beginning of the pregnancy, a blood test will inform you what your blood type is. There are four main groups: A, B, O and AB. These blood groups are either positive or negative.
What causes a blood group to be positive or negative?
A molecule named D antigen coats the surface of positive blood cells. Rhesus negative blood groups do not have D antigen.
It may be written as RhD- (negative) or RhD+ (positive) in written medical terminology. So, if your blood group is ‘A’ and you are positive, you are ‘A’ rhesus positive, or it could be written as A, RhD+.
Why could it be a problem to have a Rhesus negative mother carrying a Rhesus positive baby?
Suppose the fetal rhesus positive blood enters the maternal rhesus negative blood circulation. In that case, the mother’s blood will initiate the immune response and develop antibodies against it; this is called a sensitising event.
Potential sensitising events can occur for many reasons; for instance, an invasive procedure such as amniocentesis — when a fine needle is inserted through the abdominal wall to take a sample of amniotic fluid or an abdominal trauma such as a fall. Also, childbirth can cause fetal and maternal blood to mix.
Building an army of antibodies is a process that takes time. In the event of a sensitising event occurring, it is unlikely that there will be sufficient time to accumulate a significant amount of antibodies during the first pregnancy to harm the baby, but over time the antibodies will continue to multiply, and future pregnancies are at risk of Rhesus disease.
What is Rhesus Disease?
Antibodies that have developed to fight ‘foreign’ cells can cross to the baby via the placenta and attack the baby’s blood, resulting in a condition called Haemolytic disease of the fetus or newborn. It is treatable, but if left unmanaged, it cause’s anaemia and, in severe cases, can result in heart failure and death.
How can Rhesus negative blood during pregnancy be managed safely?
Once pregnancy has been confirmed, it is important to attend a pregnancy booking appointment. Blood samples are taken for testing to establish your blood group and whether your blood contains any antibodies.
Rhesus negative blood is managed differently from rhesus positive blood. A blood product called Anti-D is offered during pregnancy to rhesus negative women at around twenty-eight week’s gestation.
Anti-D is administered via an injection into the deltoid muscle and works by mopping up D antigens, preventing antibodies from developing. Before administering Anti-D, it is essential to take a blood sample to identify if antibodies are present.
It is possible to confirm the unborn baby’s blood group during antenatal screening by extracting DNA from the mother’s blood after eleven weeks of pregnancy. This test is called NIPT (Non-invasive prenatal testing) and is currently not widely available on the NHS. This screening test prevents the mother from having unnecessary Anti-D injections if the fetal blood and maternal blood are confirmed to be rhesus negative.
Rhesus disease is preventable, and antenatal management is essential to avoid Rhesus disease in newborns.
