If you have a negative blood group and your baby is a positive blood group we may need to give you AntiD during your pregnancy
What is my rhesus status?
When you have your first antenatal appointment you will be offered a number of routine blood tests. One of these tests is to find out your blood group (A, B, AB or O) and your rhesus status (positive or negative).
Your rhesus factor is fixed by your genes. If you're rhesus positive (RhD positive) it means that a protein (D antigen) is found on the surface of your red blood cells. If you do not have the D antigen, you will be RhD negative.
Most people are RhD positive, but this varies slightly depending on your ethnic origin. A result of RhD positive is the case for:
- 85 per cent of people of white European origin
- 94 per cent of people of African origin
- 90 per cent of people of Asian origin
Will my rhesus status affect my baby?
Rhesus status only matters if you are an RhD-negative mum who is carrying an RhD-positive baby. Your child will have inherited this from her RhD-positive dad.
If some of your baby's blood enters your bloodstream, your immune system may react to the D antigen in your baby's blood. It will be treated as a foreign invader and your body will produce antibodies against it. This is known as a sensitising event.
Sensitising is not usually harmful if it is your first pregnancy. But it can cause problems if you become pregnant again with another RhD-positive baby. The antibodies that your body made in your first pregnancy can cross the placenta and attack the blood cells of your baby.
When your baby's blood cells are attacked, it can cause anaemia. If the anaemia becomes severe, it can lead to life-threatening problems for your baby, such as heart failure and fluid retention.
After she is born, your baby's liver won't be able to cope with the volume of blood cells that need breaking down. She may then become jaundiced, which is called haemolytic disease of the fetus and newborn (HDFN), or haemolytic disease of the newborn (HDN).
In severe cases, HDFN can cause permanent brain damage and neurological problems in your baby, such as cerebral palsy, and physical or speech problems.
Rest assured that, because of routine injections of a substance called anti-D immunoglobulin (anti-D) to guard against the harmful effects of antibodies, HDFN is rare.
What do anti-D injections do?
Having an injection of anti-D can prevent your system from making antibodies. It's important to prevent antibodies from being made, because once they're produced, they stay in your blood forever.
Anti-D works by rapidly destroying any fetal blood cells in your circulation before you can make any antibodies. This means that you will not have antibodies in your system to cause haemolytic disease (HDFN) in this or your next pregnancy.
You should also have anti-D within 72 hours of any possible sensitising event, when your baby's blood could mix with yours. In the case of recurrent bleeding after 20 weeks of your pregnancy, you'll be given repeated doses every six weeks.
If you are RhD-negative and your baby's dad is RhD-negative too then your midwife is likely to offer you anti-D anyway. Your baby's dad can have a blood test to check his rhesus status. But, rarely, a dad may test as RhD-negative, while actually having traces of the D antigen, or a variant of the D antigen in his blood.
How could my baby's blood get into my blood?
Your baby's RhD-positive blood would not normally mix with your RhD-negative blood at any time during your pregnancy. However, you may experience small and unnoticed, or silent, bleeds from the placenta.
This usually happens in the last three months of pregnancy. As it's silent, you won't pass any blood through your vagina, so you won't be aware of the bleed.
More obvious ways your blood and your baby's blood could mix are because of:
- Vaginal bleeding after 20 weeks to 24 weeks of pregnancy.
- A threatened miscarriage.
- Chorionic villus sampling (CVS) or amniocentesis.
- A procedure performed to turn breech babies to a head-down position. This procedure is called an external cephalic version (ECV).
- Having a blow to your tummy.
- your midwife or doctor uses instruments to help you give birth
- you give birth by caesarean section
What happens if I already have antibodies in my blood?
Your midwife will check for antibodies when you have your routine blood tests in early pregnancy, and again at 28 weeks.
Sometimes, a previous termination, ectopic pregnancy or miscarriage may have caused a sensitising event without you realising.
If antibodies are detected in your blood, you will not be given anti-D. Ant-D is only useful in preventing antibodies from being made. It cannot remove ones that are already there. Instead, your midwife will refer you to a fetal medicine specialist.
Your specialist will monitor your pregnancy to watch for signs of anaemia in your baby. Anaemia can be treated by blood transfusions to your baby, even before she is born. Transfusion has good results in most cases.
After your baby is born, jaundice can be treated with phototherapy and more blood transfusion. These treatments help your baby's liver to break down the necessary blood cells.
Where does anti-D come from, and is it safe?
Anti-D comes from plasma, the clear yellowish fluid part of blood. The blood comes from human donors who have to pass at least two interviews before they are accepted as donors. The blood is screened for HIV, hepatitis B and hepatitis C. Only blood from areas free of variant CJD is used. The end product is also treated to inactivate any viruses.
Anti-D won't harm your baby. Occasionally anti-D can cause you to have an allergic reaction, but this is rare (less than one in 85,000 doses) and is very unlikely to be serious. However, you should stay in the health centre or doctor's surgery for 20 minutes after having the injection and say immediately if you feel unwell.
What happens after my baby is born?
When your baby is born, a sample of her blood will be taken from the umbilical cord. This is so that her blood group and rhesus status can be determined.
If your baby is RhD positive, you will be given another injection of anti-D. This must be given within 72 hours of birth so that your immune response is not triggered. Your midwife will also ask to take a sample of blood from a vein in your arm just after you give birth, to look for antibodies.
If large amounts of fetal blood are found in your system, a bigger dose of anti-D may be needed. If your baby is RhD negative and you are too, then you will not need to have anti-D.
