Preimplantation Genetic Tests (PGT)

Preimplantation Genetic Testing (PGT)

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.

Preimplantation Genetic Testing for Aneuploidy (PGT-A)

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.

Preimplantation Genetic Testing for Monogenic Conditions (PGT-M)

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.

Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR)

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.

PGT steps

  1. First Consultation and counselling with Reproductive Specialist
  2. Start IVF treatment
  3. IVF and embryo culture
  4. Embryo Biopsy and cryopreservation
  5. Results & Reports (around 3-4 weeks)
  6. Embryo Transfer


Q: Should I do PGT-A? Does it improve my chance of success?

A: PGT-A is used prior to implantation to help screen abnormality in chromosome number (known as aneuploidy) within embryos created through in vitro fertilization to reduce the chance of miscarriages due to aneuploidies. Women who are of advanced maternal age (35 years old or above), have suffered from recurrent pregnancy losses, or had repeated embryo transfers without pregnancy; or men with severe male infertility would be candidates for PGT-A to improve the chance of success.

Q: I am pregnant after PGT-A treatment. Should I still have Down syndrome screening?

A: If you have undergone PGT-A (preimplantation genetic testing for aneuploidies) as part of your IVF treatment and have received a negative result for chromosomal abnormalities, including Down syndrome, the risk of your pregnancy being affected by Down syndrome is significantly reduced. However, PGT-A testing is not a guarantee that the pregnancy will be free of all chromosomal abnormalities, including Down syndrome.

Therefore, it is still recommended that you discuss the option of Down syndrome screening with your healthcare provider, even if you have undergone PGT-A. Your healthcare provider can provide you with personalized guidance and support regarding the different screening options available, and help you determine which test is right for you based on your circumstances.



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