Pre-implantation genetic diagnosis and screening
Pre-implantation genetic diagnosis (PGD) is a very early form of prenatal diagnosis that takes place during in vitro fertilisation treatment (IVF). The embryos produced during the IVF treatment are checked in the laboratory after fertilisation to detect any abnormalities before they are implanted or replaced in the uterus.
Embryo biopsy and genetic examination
The technique used with PGD consists of two parts: an embryo biopsy, followed by a genetic examination. An embryo biopsy is carried out on all embryos (at the six to ten-cell stage) on day three after fertilisation. To do this, an opening is first made in the strong membrane surrounding the embryo (zona pellucida). One or two cells are then carefully removed from the embryo. These cells are examined in the genetic laboratory for possible abnormalities in the structure or number of chormosomes. The result of the genetic examination is known on day four or day five after fertilisation. After the examination, only those embryos that display a normal pattern for teh abnormalities checked are replaced in the uterus. If there are any surplus embryos with a normal pattern, these can be frozen. Abnormal embryos can no longer be used, except for scientific research.
Applications of PGD
PGD can be applied in patients with a serious hereditary disease. With the help of PGD it is possible to become pregnant with a child that will not inherit this disease, as the embryos that display the abnormality are not replaced in the uterus. At the LUFC PGD is used mainly for patients who display certain structural abnormalities in their chromosomes (such as translocations, deletions, etc.). Thanks to the work carried out by the centre for human genetics at UZ Leuven, these abnormalities can be sought specifically for each individual couple in their embryos. Patients with an increased hereditary risk of children with other disorders (such as Huntington's disease, mucoviscidosis, etc.) can also come to our centre for PGD, as the LUFC has a cooperation agreement with the centre for human genetics at UZ Brussels for these disorders.
In addition, with the help of PGD the sex of the embryos can also be determined and used with regard to gender-related diseases or breast cancer. It is possible, for instance, only to replace female embryos in the event of a serious hereditary disease that only affects boys or men (X-related abnormalities such as Duchenne muscular dystrophy).