Do you need PGT (Preimplantation Genetic Testing)?

A couple had regular visits to the obstetrician as she was pregnant. As part of prenatal care, the couple had thalassemia screening (thalassemia is a blood disorder that is inheritable). Results revealed that they were carriers of beta-thalassemia. Subsequent amniocentesis confirmed that the baby inherited both genes from the father and mother, and had the disease in full.

What are the couple’s options to have a healthy child in light of their genetic status? In this article, we hope to explain about ‘Preimplantation Genetic Testing’, a procedure that helps overcome this undesirable genetic inheritance.

What is Preimplantation Genetic Testing (PGT)?

‘Preimplantation’ means that genetic testing is done in an IVF (in-vitro fertilisation) process, before implantation takes place. PGT enables the selection of healthy embryos for transfer into the womb. Therefore, the couple can be sure that their children conceived through IVF are free from the disease. Although PGT is an optional test, it has been growing in use and application and especially helpful for couples whom PGT is intended for.

Types of preimplantation genetic testing services

There are several types of preimplantation genetic testing, namely, PGT-M, PGT-SR and PGT-A. As PGT-A (aneuploidy) is not allowed in Singapore, only PGT-M and PGT-SR will be discussed.

PGT-M, preimplantation genetic testing for monogenic/single gene defects – a test that screens embryos for a specific genetic mutation to avoid passing the genetic disorder to their children.

PGT-SR, preimplantation genetic testing for structural rearrangements – a test that screen embryos for structural chromosomal abnormalities such as when part of the chromosome is missing, extra, or has switched places with another.

Who is preimplantation genetic testing for?

PGT-M and PGT-SR are suitable for couples at risk of passing on serious genetic disorders to their children. These are several ways to find out if you need these tests.

1)  You should consider PGT-M (monogenic/single gene defects) if you and your spouse are diagnosed as carriers of a genetic disease, or are suffering from the genetic disease itself. Another indicator is that you have a child with a disease resulting from a single-gene disorder. Some common examples are thalassemia and muscular dystrophy.

2)  On the other hand, you should consider PGT-SR (structural rearrangements) if you and your spouse are tested to have chromosomal abnormalities (abnormal karyotype) or have had a miscarriage, where the fetus showed chromosomal abnormalities. Examples are Robertsonian translocation, inversion and insertions.

You can find a list of genetic conditions for testing through The Ministry of Health’s website here.

How safe is the procedure?

References

1. Introduction of PGT-M and PGT-SR as clinical services. Ministry of Health, Singapore.https://www.moh.gov.sg/news-highlights/details/introduction-of-pre-implantation-genetic- testing-for-monogenic-single-gene-defects-and-chromosomal-structural-rearrangements- as-clinical-services
2. Theobald, R., SenGupta, S., & Harper, J. (2020). The status of preimplantation genetic testing in the UK and USA. Human Reproduction (Oxford, England), 35(4), 986.