Embryo tested for rhesus blood group

Australian doctors have used PGD (preimplantation genetic diagnosis) to ensure that a baby shared a rhesus negative blood group with its mother. The team, based at the University of Sydney, used the technique to avoid the risk of rhesus disease, caused when the blood of a rhesus-positive baby triggers an immune reaction in its rhesus-negative mother. The doctors, who published the case in the early online edition of Human Reproduction, say it is the first reported use of PGD for this purpose.

People described as rhesus-positive - around 85 per cent of the population - have a protein called the rhesus antigen on the surface of their red blood cells, which is missing from rhesus-negative individuals. During most of pregnancy, the blood of a mother and her fetus are kept separate, but during late pregnancy or labour, a few fetal blood cells can escape into the mother's circulation. In a rhesus-negative woman carrying a rhesus-positive baby, this can provoke a response from the mother's immune system, 'priming it' to attack the fetal red blood cells in subsequent rhesus-positive pregnancies. Left untreated, this process can cause severe anaemia, and sometimes death. In the vast majority of cases, rhesus disease can be prevented by injecting a rhesus-negative woman with anti-rhesus injections throughout her pregnancy. However, of 62,000 rhesus-positive babies born to rhesus-negative mothers in England and Wales each year, around 500 have blood problems, and up to 30 will die.

The Australian team treated a couple whose second child had severe rhesus disease. Following PGD to select a rhesus-negative embryo, the mother gave birth to a healthy baby girl in 2003. 'A couple who have had a significantly affect pregnancy are faced with the dilemma of whether or not to attempt further pregnancies', said team leader Sean Seeho, adding that the tendency for the disease to worsen 'with each subsequent rhesus-incompatible pregnancy plays a major part in the decision'. The technique is only an option for couples in which the father is either rhesus-negative, or has inherited the rhesus-negative trait as well as the rhesus-positive trait.