Problems can occur if a woman’s blood is Rhesus (Rh) negative but she is carrying a baby whose blood is Rh positive. This is because Rh positive blood contains a substance called RhD antigen, which passes into the mother’s blood at birth. The mother then makes antibodies against the RhD positive blood.
There are usually no problems during a woman’s first pregnancy, but if she goes on to have another RhD positive baby, these antibodies cross the placenta and destroy the baby’s red blood cells, causing a blood disorder known as haemolytic disease that can be serious and even fatal. To prevent this, all pregnant women have their blood tested at their first antenatal visit. RhD negative women are given one or two antiserum injections during the pregnancy. However, about 38 percent of RhD negative women are carrying an RhD negative baby, so they receive this treatment unnecessarily.
So researchers at the NHS Blood and Transplant Centre in Bristol assessed a new test for predicting a baby’s blood group by “typing” its DNA in the plasma of RhD negative pregnant women. They analysed blood samples from 1,997 women taken at or before the 28 week antenatal visit. In 96 percent of cases, the correct RhD phenotype of the baby was predicted by the genotyping tests. This was confirmed by comparing the results obtained from cord blood samples taken at delivery.
The results show that fetuses of RhD negative women can be genotyped with an acceptable level of accuracy and a low rate of false positive results, say the authors. Testing would avoid unnecessary treatment in about 38 percent of RhD negative women and avert the associated discomfort, inconvenience, and risk of exposure to donor blood products that such injections entail, they conclude.
MEDICA.de; Source: BMJ-British Medical Journal