Incompatability of Blood Types and Rh Factor

I am AB-positive and my wife is O-negative. Can such a combination affect a mother and child?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

When a mother is Rh negative, as your wife is, and she gives birth to a child who is Rh positive (as could be the case), she begins to build up antibodies against future Rh-positive babies. The first baby is not affected because the antibody formation occurs mostly in the first few days after birth, in a response to the mixing of fetal and maternal blood at the time of the birth.

Mismatched blood transfusions and previous miscarriage or trauma in the pregnancy are other risks for building up antibodies.

Since 1968, we have a medication called RhoGAM, which prevents this build-up of antibodies (isoimmunization). It is generally given at about seven months (28 weeks) during the pregnancy -- to prevent early isoimmunization -- and again after the birth when the baby is Rh positive. If the baby is Rh negative, no treatment is required.

If RhoGAM is given with each pregnancy and again within 72 hours after the birth of an Rh-positive baby, your wife should have no problems with this. She will have blood tests called "antibody titers" throughout each pregnancy to make sure that she is not developing antibodies.

Another type of "incompatibility" is when the mother is type O and the baby is A or B. This is called ABO incompatibility, but when the mother is a different Rh factor from the baby, this does not occur as much. It is also a minor problem. It may result in jaundice after birth, but this is usually self-limiting and does not require exchange transfusion.

If she gets good prenatal care and receives RhoGAM at seven months and again after birth -- if your baby is Rh positive -- all should be well. In some countries, I've seen that they skip the injection of RhoGAM at 28 weeks. If this is the practice where you live, don't worry, as this early type of isoimmunization is very rare. Try not to worry.

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