PGD has been offered by the NHS for more than a decade for serious diseases that come early in childhood, like cystic fibrosis or Tay Sachs, a neurological disease.

So-called recessively inherited disorders, such as Tay-Sachs disease, cystic fibrosis and red blood cell disorders known as thalessemias are rare.

PGD is good for screening for specific genetic disorders such as cystic fibrosis and Tay-Sachs disease, and also can be used to select gender.