Preimplantation Genetic Tests

Preimplantation Genetic Testing (PGT) is a genetic testing procedure performed before an embryo (obtained via IVF + ICSI) is transferred into the uterus. Its purpose is to identify potential genetic abnormalities in the embryos. It is used to assess whether the embryos carry chromosomal or genetic abnormalities. Through this testing, embryos with normal genetic profiles can be selected for transfer into the uterus.

The different types of PGT are introduced here.

Embryos with abnormal chromosome numbers (aneuploidy) have a reduced likelihood of successful implantation when transferred to the uterus, which is one of the most common factors contributing to the failure of in vitro fertilisation (IVF) treatment. Conducting Preimplantation Genetic Testing for Aneuploidy (PGT-A) helps identify whether embryos have the correct number of chromosomes.

Furthermore, embryos with abnormal chromosome numbers, even if they successfully implant, are more likely to develop into fetuses with congenital defects. One common example is Down syndrome, which occurs when there is an extra copy of chromosome 21. It's worth noting that even couples with normal chromosomes or genes undergoing IVF treatment may produce abnormal embryos, and the likelihood of this increases with the woman's age. Therefore, older women undergoing IVF treatment have lower success rates and higher rates of miscarriage.

During the testing for aneuploidy, doctors select embryos with the correct chromosome numbers (euploidy) for transfer, increasing the chances of successful implantation and reducing the risk of early miscarriage.

If either partner is a gene carrier of a known single-gene disease, and the gene has a chance of seriously affecting the health of the next generation, PGT-M can be considered to extract a few cells for testing before embryo transfer. This helps to prevent related diseases from being passed on to the next generation.

If either partner is a known carrier of a balanced chromosomal translocation, it may lead to the emergence of genetically abnormal eggs or sperm, causing miscarriage or implantation failure. The couple may consider PGT-SR, where a few cells are extracted before embryo transfer for chromosomal rearrangement testing, in order to select embryos with normal chromosomes for transfer.