Currently, all women who test RhD negative at routine antenatal checks are given one or two antiserum injections during the pregnancy. But scientists say an easy, rapid test to assess the baby's RhD status means more than a third of RhD negative women can skip the injections. Trial results of the test are reported in the British Medical Journal.
The RhD factor is one of multiple blood cell surface markers, including the best known A/B/O blood group markers. Knowledge of blood-group status is important because transfusion of donor blood with cell surface markers (such as RhD-positive blood) to a recipient who lacks them (RhD-negative) can cause an immune reaction to be mounted against the foreign cells.
It is the same reaction that is found in a person who reject tissue transplants. The same problem can arise when a RhD-negative mother gives birth to a RhD-positive baby; mixing of the maternal and fetal circulation around birth.
However, a majority of RhD-negative mothers will actually be carrying a RhD-negative fetus and so receive the immunoglobulin treatment unnecessarily.
"The introduction of fetal genotyping followed by the withholding of antenatal anti-RhD prophylaxis from mothers with an RhD negative fetus would result in about 36 percent of women being saved from unnecessary exposure to human blood products, inconvenience, and discomfort," the authors wrote.
Researchers from the International Blood Group Reference Laboratory in Bristol used an Applied Biosystems Prism 7900 HT instrument to do real-time quantitative test on maternal and fetal DNA extracted from pregnant women's blood.
Researchers now say such tests could be more beneficial earlier in pregnancy and should be done after about 26 weeks of gestation. The findings are important because of the concerns over anti-serum injections derived from blood products, which could be a source of infections such as hepatitis C.
