Pre-implantation genetic diagnosis is the examination of an extracorporeal embryo for known serious genetic diseases (which are carried by one or both parents) or for chromosomal disorders which are very likely to lead to a miscarriage or stillbirth.
Artificial extracorporeal fertilisation is necessary for the performance of PGD. Here, egg cells are retrieved from the ovaries (generally after hormone stimulation).
The fertilisation procedure must take place through intracytoplasmic sperm injection: an individual sperm cell is transferred inside the egg cell. After fertilisation occurs, the development of the embryo starts outside the body in the form of multiple cell divisions.
During PGD, cells are removed from the embryos outside the body for molecular genetic or chromosomal examination.
Only embryos without the serious genetic disorders or chromosomal disorders in question should be transferred into the uterus.
The embryonic cells removed come from the “jacket cells” (trophectoderm cells) of the embryo. They can no longer develop into a complete embryo themselves, but form the placenta in the womb, for example. Therefore, they contain the same genetic information as the embryo itself. Their removal does not harm the embryo.
The removal of the trophectoderm cells (“trophoblast biopsy”) takes place using PGD methods on the embryo (the so-called blastocysts) five days after fertilisation: cells are aspirated through the protective shell (zona pellucida) from the outer layer using a glass capillary. A tiny opening is created in the zona pellucida with laser technology.