Steps involved in PGT (Preimplantation Genetic Testing)

In our earlier article, we explained about who preimplantation genetic testing (PGT) is for—do have a look if you have not! To recap, PGT is helpful for couples at risk of passing down genetic disorders to their children. Through PGT, healthy embryos are identified and selected for transfer into the womb, ensuring that the resulting child is free from the disease.

Here are the steps involved in PGT, specifically for PGT-M and PGT-SR, that you can be aware of.

Pre-PGT preparations

1) Clinical Diagnosis

During consultation, your fertility specialist will discuss with you on the need for PGT. A clinical diagnosis is made based on you and your spouse’s DNA analysis report which shows whether you carry the gene that causes the condition.

2) Genetic Counselling

During the counselling, your referred genetic counsellor will explain details of the disease, your genetic risk assessment and likelihood of occurrence in pregnancy. The implications and limitations of PGT such as possible outcomes are discussed. Your alternative reproductive options are also mentioned.

3) PGT feasibility test & PGT workup preparations

Once the PGT laboratory receives your reports and consents, they will evaluate whether PGT is suitable for your condition (feasibility test). After approval, the centre will require blood samples from you and your spouse for PGT workup preparations (only applicable for PGT-M). Following the completion of workup preparations, your IVF cycle can then begin.

The PGT process – IVF cycle, biopsy and PGT analysis

PGT-M and PGT-SR are performed as part of an IVF cycle. The eggs are retrieved from the woman and are fertilised with the husband’s sperm. The embryos develop over the course of five to six days in the laboratory. Good-quality embryos, now called blastocysts are selected for biopsy. Biopsy is the step where a few cells of the blastocysts are gently removed (Figure 1). The cells are loaded into a tube and sent to the PGT laboratory for analysis. Meanwhile, the blastocysts are frozen.

• Figure 1: Illustration of trophectoderm biopsy on a blastocyst.

The PGT laboratory performs the analysis specific for the genetic condition being tested for. After the PGT results are obtained, unaffected blastocysts are chosen for transfer into the womb in a subsequent frozen embryo transfer cycle.

In the event of a successful pregnancy, you are advised to go for prenatal screening (amniocentesis or chorionic villus sampling, CVS) to confirm the PGT diagnosis and ensure that the fetus is well.