Your blood test will confirm whether your blood is rhesus positive or rhesus negative.
People with rhesus positive blood have a substance known as “D Antigen” on the surface of their red blood cells but people with rhesus negative blood do not. This can cause problems if a woman has rhesus negative blood and her baby has rhesus positive blood. If any of the baby’s blood gets into the mum’s blood stream, during birth, bleeding or an injury, the mum’s immune system can start to create antibodies against the rhesus antigen. The name for this is “sensitisation”. This is not a problem in first pregnancies, but in subsequent pregnancies there is a risk that these antibodies can attack the baby’s blood cells and cause a serious condition called haemolytic disease of the newborn. This can result in the baby suffering from jaundice and anaemia, and can also be a potential cause of miscarriage or stillbirth.
If we confirm that your blood group is rhesus negative, we will offer you a further blood test. Genetic information (DNA) from the unborn baby can be found in the mother’s blood, which allows the blood group of the unborn baby to be checked without any risk. It’s usually possible to get a reliable result from this test after 12 weeks of pregnancy, which is long before the baby is at risk from the antibodies. If your baby is rhesus negative, they’re not at risk of rhesus disease and no extra monitoring or treatment will be necessary. If your baby is rhesus positive, we will offer anti-D injections.
Anti-D injections deal with any rhesus positive antigens so that the body doesn’t produce the antibodies, preventing mum from becoming sensitised. If your blood tests show that you need anti-d injections, your midwife will let you know, and you’ll receive the injection at 28 weeks. If you experience any vaginal bleeding, falls or bumps to the abdomen during pregnancy, it’s important to let your midwife now as you may need an additional injection.