Blood group incompatibility in pregnancy
9 Jul 2012

Blood group incompatibility in pregnancy

2 mins to read
Naturopath Stephanie Hamilton explains the issue of blood group incompatibility in pregnancy.


Blood groups and the Rhesus factor
If you have ever given blood you will know what blood type you are: A, B, AB, or O. You may also know if you carry the Rhesus factor, making you a Rhesus positive blood type if you do, and a Rhesus negative blood type if you don’t. 

The Rhesus factor, also known as RhD, is a protein that is either present or absent on the surface of a person’s red blood cells. For example, A+ means that the blood is type A and each blood cell has the Rhesus factor.

Genetics determines a person’s blood type and whether the Rhesus factor is present or absent. The majority of the population is RhD-positive with approximately 85% of people carrying this factor. The remaining 15% are RhD-negative.

What are the concerns in pregnancy?
Rhesus incompatibility can happen in pregnancy if a RhD-negative mother and a RhD-positive father conceive a RhD-positive baby. Rhesus incompatibility cannot occur in a RhD-positive woman.

The diagnosis of Rhesus incompatibility usually results from routine testing revealing anti-RhD antibodies in a RhD-negative mother.

In the situation of a RhD-negative woman carrying a RhD-positive foetus, the mother’s body considers the foetal RhD-positive cells a threat and an immune response is triggered. This response begins in the first RhD-positive pregnancy, when very small numbers of the baby’s red blood cells actually escape into the mother’s circulation. These cells are rapidly destroyed before they can provoke antibody production. At the time of birth, a much larger transfusion of foetal blood into the mothers circulation can occur as the placenta is compressed and separated. This is likely to stimulate the production of antibodies after birth which, should the woman become pregnant again, will cross into the placenta and attack the future unborn baby’s blood cells if they are Rh-positive, causing haemolytic disease of the newborn (HDN) or RhD disease.

Haemolytic disease of the newborn (HDN)
Haemolysis means the destruction or rupture of red blood cells. When this happens, the baby’s blood cannot carry sufficient oxygen. Babies can survive with this condition but are often born with anaemia and jaundice. In severe cases the lack of oxygen can cause heart failure while the baby is still in the womb and miscarriage can occur. However, these severe cases are now very uncommon in developed countries due to the injection that is available.

What can be done to prevent HDN?
Part of any prenatal screen is to check the blood type and Rhesus factor of the mother  wanting to conceive. An injection is routinely given to RhD-negative women during pregnancy and immediately after they give birth to a RhD-positive baby to prevent their immune systems from making the antibodies by ‘hiding’ the Rhesus protein on any blood cells from the unborn child that have escaped into the mothers’ circulation. The injectionhas been shown to be 99% effective. Your doctor will advise on when to have this injection during your pregnancy.

References available upon request



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