Rhesus Factor And Pregnancy
Human blood is grouped into four types: A, B, AB, or O. Each letter refers to a type of antigen found on the surface of red blood cells. For example, Type A blood has antigens known as A-antigens. Each blood type is also grouped by its Rhesus factor (Rh).
Rhesus is another type of antigen on the surface of red blood cells.
Blood is either Rh positive (Rh+) or Rh negative (Rh-).
Most people who have the Rhesus factor are Rh positive and those who don’t have the Rhesus factor are Rh negative.
How Do I Know My Blood Type?
If you don’t know your blood type you can ask your care provider to refer you for a blood typing test. Globally, the most common blood types are O+ and A+. Approximately 85% of the population has the Rh factor and the remaining 15% is Rh negative.
The Rh factor is passed down from parents’ genes to their children. If a mother is Rh negative and the father is Rh positive, their baby can inherit the Rh gene from the father and be either Rh positive or Rh negative. The Rh positive gene tends to be stronger and will take over, even when paired with a Rh negative gene. So if the mother is Rh negative and the father is Rh positive, the baby is likely to be Rh positive. If the mother and father are both Rh negative, the baby will also be Rh negative.
How Can The Rhesus Factor / A Negative Blood Group Be A Problem?
Problems with the Rhesus factor occur when the mother's Rh factor is negative and the baby's Rh factor is positive. This is called Rh incompatibility. These problems usually don’t occur in first pregnancies but will arise in subsequent pregnancies.
If the baby’s Rh positive blood manages to mix with the mother’s Rh negative blood during pregnancy or labour, the mother’s blood will create antibodies against the Rh factor, as though it were a harmful substance. This means the mother becomes ‘Rh sensitised’.
The Rh antibodies can cross the placenta and attack the baby’s blood, destroying the red blood cells. This causes hemolytic anaemia, which is when the red blood cells are destroyed faster than they can be replaced. If this occurs, bilirubin (a by-product of red blood cell breakdown) builds up in the baby’s bloodstream. After birth, the baby can appear lethargic, have low muscle tone, and yellowing of skin and eyes (jaundice).
Red blood cells carry oxygen to all parts of the body. If there aren’t enough red blood cells, the baby might not receive enough oxygen. Fetal hemolytic anemia can lead to serious illness and potentially death.
How Does Rh Sensitising Happen During Pregnancy
During pregnancy, the mother’s and baby’s blood systems are separate. However, during pregnancy, labour or birth, a small number of red blood cells from the baby can cross the placenta and enter the mother’s blood. This can also happen if the mother experiences:
- Amniocentesis (sampling of amniotic fluid via a needle inserted through the abdomen)
- Chorionic villus sampling (sample from the placenta via needle inserted into the abdomen or through the cervix)
- Any bleeding during pregnancy
- Any blunt trauma to the abdomen during pregnancy
- A pregnancy that ends in miscarriage, termination or is ectopic (implanted in the fallopian tube instead of the uterus), or
- If baby is breech and manual rotation is attempted before labour
This Is My First Pregnancy With Rh Factor – Are There Any Concerns?
In most situations it takes time for a woman’s body to produce antibodies once sensitisation has occurred. This means in the first pregnancy with an Rh positive baby there are rarely serious problems, as the baby is born before many antibodies are developed.
However, during the first pregnancy with Rh factor, it is necessary for a mother to have treatment, if she intends to have more children. Any future pregnancies with a Rh positive baby are at risk, if the mother’s antibodies cross the placenta and attack the baby’s blood cells.
How Can This Be Prevented?
Nothing can be done about the Rhesus factor of your blood, or your partner’s. If your blood test comes back with a Rh negative result, your care provider will request that your partner’s blood type be tested. If your partner is also Rh negative, there’s nothing to be concerned about. If your partner’s results are Rh positive, further testing might be needed.
Your care provider can organise several blood tests during your pregnancy, to monitor the antibody levels in your blood. After birth, your baby’s blood will be tested for its type. If your baby has Rh positive blood, you will be offered an Anti-D injection within a few days of the birth. This will prevent antibodies from forming in your bloodstream. When given to a non-sensitised Rh negative person, the Anti-D targets any Rh positive cells in the bloodstream and prevents the production of Rh antibodies. Anti-D isn’t useful if you have already become Rh sensitised.
If you experience any bleeding during pregnancy, or if you have an amniocentesis, miscarriage, ectopic pregnancy or termination, make sure your care provider is aware as soon as possible. All of these might present opportunities for the blood of the fetus to mix with yours, and it will be unclear in most of those cases as to which blood type the baby has.
Some care providers recommend giving Rh negative women Anti-D injections without doing blood tests to detect antibodies. This might prevent antibodies from forming but it’s not without risks. The Anti-D is a blood product (which has its own risks), and in rare cases can cause allergic reactions.
If your pregnancy is normal and healthy you might opt not to have Anti-D injections until after the birth, when your baby’s Rh factor is known. The chances of blood mixing in a normal, healthy pregnancy are very slim, and if your blood tests show no antibodies present, you might prefer to find out whether it’s necessary before having the injections.
I Have Already Formed Antibodies Against The Rhesus Factor
If your blood has already formed antibodies you’ll need to be closely monitored for any signs your baby is anaemic. If your baby has mild anaemia and it’s safe to do so, your baby should be able to go full term. If the anaemia is severe, your baby might need to be born early or, in rare cases, be given a blood transfusion through the umbilical cord while still in your uterus.
If Rh incompatibility occurs, specialist care your baby might require after birth includes:
- Blood transfusions
- Hydrating fluids
- Electrolytes to regulate metabolism
The risk of antibodies forming exists with every pregnancy, even if you have been given the Anti-D injection in your previous pregnancy. It’s important to make sure, with any future pregnancies, that your blood group is known to all care providers you deal with. Being informed and aware of your blood group will give you peace of mind, and help you make the best choices for you and your baby.
Recommended Reading: Jaundice In Newborns – The Truth About Jaundice.
Also see: “Anti-D in Midwifery: Panacea or Paradox,” by Sara Wickham