Preimplantation genetic diagnosis (PGD) is an early testing method for oocytes and embryos that helps prevent the birth of children with genetic disorders. The method combines assisted reproduction technologies, embryology and genetics. PGD is the earliest possible prenatal study and is used together with IVF/ICSI procedures, when embryos with incorrect genetic codes are being diagnosed prior to being returned to the uterus. Only embryos with correct genetic codes are selected for embryo transfer. Should pregnancy result, this offers certainty that the risk of inborn genetic conditions in the developing embryo is significantly reduced. PGD may be applied to increase the implantation index of embryos, thus increasing the chance of pregnancy and the eventual birth of a healthy child. It is used to screen egg cells, spermatozoa and embryos for chromosomal anomalies and set genetic disorders, as well as to ascertain the sex.
These are the major indications for preimplantation genetic diagnosis:
- Mother age over 34;
- Parent age over 39;
- Chromosomal anomalies such as translocation, inversion or other chromosomal or genetic disorders;
- Two or more spontaneous abortions;
- Two or more unsuccessful IVF procedures;
- Men with abnormal analyses of spermatozoal penetration or chromatin structure.
aspiration of one blastomer for analysis
The benefits of preimplantation genetic diagnosis include:
- Selection and transfer of embryos lacking definite chromosomal abnormality data;
- A reduction of spontaneous abortions;
- A reduction of multiple pregnancies;
- An increase in embryo implantation rates;
- An increase in healthy birth rates.
Risks in PGD include:
- Embryo damage (under one per cent)
- Misdiagnosis (under ten per cent)
- Erroneous designation of abnormal embryos as normal (under three per cent)
- Erroneous designation of normal embryos as abnormal (under ten per cent)
- Embryo transfer prevention where embryonic abnormalities are determined (up to 20 per cent).