ABSTRACT
As a medical geneticist, one first considers preimplantation diagnosis (PID) in the context of the established methods of prenatal diagnosis (PND). PID has a number of obvious advantages: only non-affected embryos are transferred to the woman’s uterus; no abortion is needed in the event of a pathological result, and there is no need to begin what amounts to a pregnancy on probation as is the case if the health of the foetus has to be determined by conventional PND. Selection of gametes opens up intriguing prospects for the prevention of inherited diseases. Whereas gene typing of individual sperms is not possible, it has been successfully carried out, by an indirect approach, on oocytes. In the absence of crossing-over, the first polar body will be homozygous for all alleles not contained in the oocyte and the second polar body. In vitro fertilisation has created an opportunity to perform genetic studies on polar bodies, blastomeres or trophoectodermal cells.
