Rhesus Negative women
The blood group of most women is Rhesus positive (Rh+ve). If the mother is Rhesus negative (Rh-ve) and the father is Rh+ve, the foetus can also be Rh+ve. In such cases some blood from the foetus can pass to the mother and cause her to produce antibodies. These antibodies can destroy the foetal blood cells. Usually the condition is mild but in some cases the foetus can become very anaemic and even die.
To stop the mother from making antibodies, Rh-ve women are normally given a drug called anti-D whenever a baby’s blood cells may have crossed into her circulation. This may happen at the time of delivery, but can also happen after a CVS or amniocentesis earlier in pregnancy.
Anti-D is made from donated blood. Its production is strictly controlled to ensure that there is virtually no chance of the mother receiving a viral infection from the donor. The risk of an infection is estimated at 1 in 10 billion doses. Donor blood is not specifically checked for nvCJD (mad cow disease), but the blood used to make anti-D comes from countries outside the UK, where this illness has not been a problem.
If you have a CVS or Amniocentesis and are Rh-ve, there is a risk that you may produce antibodies to RhD. If you know that you are Rh-ve, we will offer to give anti-D immediately after the CVS or amniocentesis. If we are not sure of your blood group we shall check this first and ask you to return to the clinic for anti-D if the result shows you are RhD-ve. Anti-D should be given within 72 hours of the test to be effective.
As the RhD factor is inherited, this means that if both parents are Rh-ve, the baby must be Rh-ve as well. In this circumstance, there is no risk of the mother becoming sensitised after CVS or amniocentesis.
In many circumstances, anti-D is given when we are unsure of the baby’s RhD status. Many studies have shown that Anti-D does not harm the development of a baby in the womb. Anti-D is offered in these circumstances because of the risks of a baby developing haemolytic disease.