GENETIC DIAGNOSIS

Pre-Implantation Genetic Diagnosis (PGD) and Pre-implantation Genetic Screening (PGS) are relatively new diagnostic procedures first performed in 1988. Since then, through the use of PGD or PGS and selection techniques in approximately thirty clinics worldwide, over 2,000 children have been born free of genetic defects that were present in their family gene pool.

For couples at risk of having children with an inherited disease, Pre-Implantation Genetic Diagnosis (PGD) is a new approach to prevent the birth of affected children. Other methods of prenatal diagnosis such as amniocentesis or chorionic villus sampling (CVS) involve taking samples from an established pregnancy. If the fetus is diagnosed as affected, couples then have to decide whether or not to terminate the pregnancy. Some couples may have to undergo several terminations in their attempt to produce a healthy child. With PGD or PGS, In Vitro Fertilization (IVF) treatment is used to screen early embryos (within a few days of conception) for the inherited defect causing the disease. Couples can then choose to have only those embryos identified as free of the disease implanted in the woman's uterus, knowing that any resulting pregnancy should be normal. In its ability to intervene before the pregnancy is established in utero, PGD offers patients a great advantage over both amniocentesis and CVS.

Pre-Implantation Genetic Diagnosis is used during an IVF cycle to identify specific embryos that carry abnormal genes. PGD can also be used to help select embryos of a particular sex, usually to avoid sex-specific diseases, but it can also be performed for family balancing. PGD is normally recommended for couples when one or both of the parents are a known carrier of a genetic disease (i.e. hemophilia or cystic fibrosis). PGD is usually performed after a woman's eggs have been fertilized by her partner's sperm, but before the embryos are transferred back to the uterus. When the fertilized egg has reached between the six- and ten-cell development stages, one cell (known as blastomeres) are gently removed from each embryo using a microsurgery technique similar to that used in ICSI. The DNA from the removed blastomeres is then analyzed for genetic diseases or chromosome numbers. If any abnormal is found, the results will be carefully explained to the potential parents. It is then for the parents to decide which embryos they wish to transfer. This is an important and sometimes difficult decision, which has to be made in a short amount of time on the day of transfer. We recommend, therefore, that patients and families electing for PGD or PGS talk over the possible outcomes beforehand such that they have adequate time to think through all of the potential issues.