In the news

Australian doctors have reportedly used pre-implantation genetic diagnosis (PGD) to screen embryos for their blood group, to ensure that the embryo selected for implantation shared a rhesus negative blood group with the mother (see BBC news report). Women who are rhesus negative but have rhesus positive babies will produce an immune response termed alloimmunization against the ‘foreign’ rhesus blood cell markers when the maternal and fetal blood mixes, mostly during labour. The severity of this response increases with each subsequent rhesus-positive pregnancy, and can cause severe and potentially fatal anaemia in the new baby. In the vast majority of cases (around 99%) this situation can be prevented by giving rhesus negative mothers an anti-Rhesus injection during pregnancy to prevent the production of potentially dangerous antibodies; babies affected before birth can also be treated by blood transfusion in the womb. In England and Wales, around 62,000 such births occur each year; around 500 babies develop haemolytic disease of the newborn and up to 30 of these babies will die, with a similar number having developmental problems (see European Society of Human Reproduction & Embryology press release).

Dr Sean Seeho of the Royal North Shore Hospital in Sydney where the procedure was carried out said: "A couple who have had a significantly affected pregnancy are faced with the dilemma of whether or not to attempt further pregnancies". In this instance PGD was used to select an embryo for a couple whose second child had suffered from severe haemolytic disease due to a maternal alloimmunization response. A subsequent healthy rhesus-negative child, implanted following the PGD selection procedure, was born in 2003. The BBC claims that the use of PGD in this case “enabled a couple to have a healthy child who might otherwise have died” but it should be noted that even without PGD this couple could still have had a perfectly healthy child; a naturally conceived fetus would have had a 50% probability of being Rhesus negative anyway. The technique is also only viable for couples where the father was heterozygous for the Rhesus blood group; where the father is homozygous for the Rhesus blood group, all his offspring would be Rhesus positive and so PGD to select for a Rhesus negative fetus would be futile.