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.
The retrieved cells (trophectoderm cells or trophoblast cells) are frozen and forwarded for genetic examination. This examination generally takes 1-2 days (frequently more).
For this reason, the embryo (the blastocyst) has to be frozen because this time delay means that the uterine lining is no longer receptive for the embryo.
The freezing technique is vitrification. This technique can also prevent permanent damage to the embryo (according to our current level of knowledge), but approx. 5-8 % of the thawed embryos do not survive the procedure.
The results of the genetic analyses are presented to the couple from a medical point of view (human genetics and reproductive medicine) and weighed up. At the same time, the very rare possibility of false diagnoses during the PGD is also weighed up.
Following this, consent is provided for the transfer of one or two embryos.
The transfer of one or two embryos which do not feature the examined genetic disorders is then either performed in a completely natural cycle five days after ovulation or in a cycle in which the uterine lining is built up by oestrogen tablets.
The fist step is a genetic consultation and examination which is performed in the Institute for Human Genetics in Munich by Dr Nevinny.
Human Genetics, Munich
The second step is an examination and consultation with us to explain and establish the reproduction framework for the entire treatment.
Then comes the application of the couple or the patient to the Bavarian ethics committee which has to check and approve the requirements for the performance of PGD in the present case.
The payers currently do not bear the costs for PGD treatment or only in exceptional cases. This also relates to the costs of the necessary basic treatment for an artificial insemination (ICSI), which can only be borne if there is an indication in the form of a reduction in the sperm quality.
An application is sensible in any case and will be supported by us.
The experiences and results to date are summarised in the presentation by Dr U. Noss (talk at the “Joint FERRING FORUM” of reproductive medicine and paediatric endocrinology
on 24th April 2015 in Hamburg). The examination has now been performed on more than 1000 embryos.
Update PGD 2011-2015.PDF