Pregnancy and rhesus disease

Dr Trisha Macnair responds

Because you're rhesus negative, there's a risk that any babies you have may suffer from haemolytic disease of the newborn, also known as rhesus disease or blue baby syndrome.

However, this will only occur if your partner is rhesus positive. If this is the case then your unborn baby may have inherited its father's rhesus positive status and there'll be a mismatch between you and your baby's blood.

There are usually no problems with a first pregnancy with a rhesus positive baby, because the mother is first sensitised to rhesus positive blood during the birth of the baby. It's in further pregnancies that there may then be a risk to the baby.

But, there may be a risk in the first pregnancy if the woman has had a previous miscarriage or termination, if she has had an invasive procedure during pregnancy such as amniocentesis or chorionic villus sampling (CVS), or if she has mistakenly been given rhesus positive blood in a transfusion.

How rhesus incompatibility develop

People who are rhesus positive have a compound called D antigen in their blood, while people who are rhesus negative don't.

During pregnancy, and especially during labour, tiny amounts of the baby's blood crosses the placenta into the mother's bloodstream. If the baby is rhesus positive and has the D antigen, then this triggers a reaction in the mother who'll start making antibodies to the D antigen.

In subsequent pregnancies, these antibodies may go back across the placenta and attack the blood of the baby. The result is destruction of the foetus's red blood cells, which may result in a condition called hydrops fetalis and stillbirth.

Treatment is simple

Fortunately problems are rare these days because of the use of anti-D (Rh) immunoglobulin to prevent sensitisation to rhesus factor. An injection of this immunoglobulin is given to the mother soon after the birth of a rhesus positive baby. It acts by mopping up any of the baby's rhesus positive blood cells which have crossed into the mother, and destroying them before they sensitise her.

If given with 72 hours of birth it's 99 per cent effective in preventing sensitisation.

Little risk in this pregnancy

This means that there's probably little risk to you or the baby from rhesus incompatibility in this first pregnancy. Your blood should have been checked to see if you're producing antibodies to rhesus factor at the first antenatal visit (all pregnant women are checked at this time).

You may be checked again at 28 and 36 weeks of pregnancy. Whether or not these tests are normal you need to be vigilant about your health like every pregnant woman. If you're making antibodies, you and your baby may need special care for the rest of the pregnancy.

After the delivery you should ensure the doctor at the hospital is aware that you're rhesus negative and you're given anti-D.

If you become pregnant again you should be protected if you've had anti-D, but those looking after you will probably want to test your blood at regular intervals to check for production of antibodies against rhesus and may want to do occasional extra checks on the baby just to be sure.