Q&A Rhesus blood grouping explained
Please can you explain the Rhesus factor to me. I am expecting my second child, and I’ve heard it can be an issue this time around. Will I be tested as routine, or do I have to ask specifically? And how will the doctor know what my husband’s status is, or doesn’t that matter? I find the whole thing quite confusing.
DR KOLL ANSWERS: The Rhesus antigen is one of many in our blood. The other well-known antigens are the A and B antigens. We inherit these antigens from our parents. If you inherited the A antigen from one of your parents, your blood group will be A. Similarly, if you inherited a B antigen, you will be group
B. If you inherited both A and B, you will be group AB, and if you inherited neither A nor B, your blood group will be Group O.
The Rhesus antigen is known as big D. If you inherited a D antigen from either one or from both your parents, you will be Rhesus positive. If you did not inherit the D antigen from either of your parents, you will be Rhesus negative.
If you do not have the Rhesus antigen (so you’re Rhesus negative), and you are given a blood transfusion from a Rhesus positive person, your body will produce antibodies that will attack and destroy the foreign red blood cells.
This is why a Rhesus negative person cannot get a blood transfusion from a Rhesus positive person.
If you are Rhesus negative and your partner is Rhesus positive, there is a chance that your baby might inherit your partner’s D antigen and thus be positive too. If your baby is positive, and some of baby’s blood gets into your bloodstream, your body will make anti-D antibodies that will attack your baby’s blood, destroying red cells and making Baby anaemic.
The most likely time for baby’s blood to get into your bloodstream is at the time of delivery. This is why, if you are Rhesus negative, we test baby’s blood immediately after birth, and if Baby is positive, we give you an injection of anti-D antibodies. These antibodies coat any of baby’s red blood cells that may be in your bloodstream and thus hide them from your body’s immune system. Your body’s immune system does not make any antibodies and thus your next baby will not be affected even if he or she is Rhesus positive. There are also other times during the pregnancy when baby’s blood can get into your bloodstream.
If you suffer a miscarriage, have a bleed during the pregnancy or have an amniocentesis or chorionic villus sample, some of Baby’s blood may get into your bloodstream. If any of these things happen, and you are Rhesus negative, you will be given an injection of anti-D to prevent antibodies from developing and thus protect your next pregnancy. Occasionally, in the third trimester, Baby’s blood gets into your system for no obvious reason. If you’re Rhesus negative, you’re given anti-D injections once or twice in the third trimester.
Rhesus disease used to be a fairly common condition, causing adverse outcomes in pregnancy. Thankfully, the preventative measures mentioned above have been very successful in preventing Rhesus disease, and severe Rhesus disease is a very rare condition now. Just to recap. The only time that Rhesus can be a problem is if the mother is negative and the father positive. If the mother is positive, it does not matter what Rhesus group the father is.
All patients will have their Rhesus group checked in pregnancy.
If you are negative, your partner’s group will usually be tested.
If he is negative, there is no risk to baby, but the baby’s blood group will still be checked after delivery, just as a precaution. If he is positive, the above precautions will be taken. ●