Preimplantation Genetic Testing
Preimplantation Genetic Testing refers to procedures performed to determine the normality of the embryo prior to implantation to prevent a pregnancy affected by a genetic condition or chromosomal disorder.
These tests provide an alternative to diagnostic procedures done after conception such amniocentesis or chorionic villus sampling, which are frequently followed by the difficult decision of pregnancy termination, if results are unfavourable.
This technique involves the biopsy of cells from the embryo, either at Day 3 or at blastocyst stage and subjecting the cells to tests. It encompasses two distinct procedures called Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS).
Preimplantation Genetic Diagnosis (PGD)
When one or both parents have a known genetic abnormality, PGD is performed on the embryo to determine if it also carries the same abnormality. Only the embryo that is free of the abnormality is subsequently transferred.
PGD is offered for 3 major groups of disease:
- sex-linked disorders, diseases that are passed to the child through a mother who is a carrier such as haemophilia.
- single gene defects, diseases that are caused by abnormality in a single identifiable gene. The most common in Malaysia is thalassaemia.
- chromosomal disorders, which is due to a variety of chromosomal rearrangements, such as translocation.
Thalassaemia is an inherited blood disorder where due to the instability of the wall of the red blood cell (RBC), the patient constantly suffers from anaemia (low levels of haemoglobin, the oxygen carrying part of the RBCs). It is estimated that one in 20 Malaysians are thalassaemia carriers, which is about 1.5 million Malaysians, affecting mainly the Chinese. If both parents of a child are thalassaemia carriers, there is a 25% chance the child have major thalassaemia, which is a serious condition. PGD now offers a chance for the couple to have a disease free child by testing the embryos created from IVF for the thalassaemia gene before being implanted into the womb. This also effectively stops the thalasaemia gene from being passed down to the subsequent generations.
Preimplantation Genetic Screening (PGS)
PGS refers to the procedure where embryos from presumed chromosomally normal genetic parents are screened for aneuploidy (abnormal chromosome numbers).
PGS can be offered to the following:
- Women of advanced maternal age
- Couples with history of recurrent pregnancy loss
- Couples with repeated IVF failure
- Male partner with severe male factor infertility
Aneuploidy is a major cause of IVF failure. By selecting chromosomally normal embryos, PGS has been shown to:
- Improve implantation rates
- Reduce spontaneous miscarriage
- Increase ongoing pregnancy rate
- Enable single or double embryo transfers, decreasing the number of high-risk multiple pregnancies
Next Generation Sequencing (NGS)
Developed in 1990s, Preimplantation Genetic Testing has undergone rapid advances. NGS is the latest technological breakthrough for providing comprehensive and accurate screening of all 24 chromosomes for selection of a healthy embryo. Sunfert will be the first in Malaysia to offer this technology.
The advantage of NGS is that it is quicker (sample to answer in approximately 12 hours) and cheaper, while remaining just as sensitive as other methods of screening. This technology has recently been validated for embryo screening and has achieved FDA approval.