Preimplantation genetic diagnosis (PGD) is a technique for testing the genetic make-up of embryos before they are used in treatment. PGD has been carried out in the UK (under HFEA licence and regulation) for many years, but in 2008 Parliament created laws which restrict the circumstances in which such techniques can be used. The law now allows embryo testing in the UK only for the following purposes:
Excluding serious genetic abnormalities
PGD can be used to exclude a gene, chromosome or mitochondrion abnormality. This might be an abnormality that causes miscarriage or stillbirth, in which case the purpose of the testing is to give the best chance of a successful pregnancy. Alternatively, it might be an abnormality that would affect any child born, in which case the purpose of the testing is to choose an embryo that is free of the disorder in question (there must be a particular risk and the abnormality must carry a significant risk that the child will develop a serious disability, illness or condition).
Sex selection as a means of excluding abnormalities
Where a serious condition or illness cannot be tested for directly but affects one sex significantly more than the other, PGD can also be used for sex selection (i.e. choosing to put back only male or only female embryos). These are the only circumstances in which sex selection is permitted in the UK.
PGD can also be used to select an embryo to conceive a child who will be a tissue match for a sick sibling, but only where the child conceived would be a tissue, cord blood or bone marrow donor (PGD cannot be used to conceive a child to act as an organ donor).
Suspected embryo mix-ups
Where a question has arisen about who are the biological parents of an embryo, PGD can also be used to establish biological parentage before the embryo is used in treatment.