All About Preimplantation Genetic Testing By Dr Parul Agarwal

PGT is a primary diagnostic tool to prevent any known genetic disorder transmission.

Preimplantation genetic testing (PGT) allows the transfer of genetically normal embryos. Dr Parul Agarwal, Director – IVF and Fertility at Cloudnine Group of Hospitals, Noida, shares that this technology has become integral to Assisted Reproductive Technology (ART) procedures.

WHO ARE THE GOOD CANDIDATES FOR PGT?

1. Couples with a previous pregnancy or children with an inherited genetic disorder.
2. Women who have had two or more miscarriages due to chromosomal abnormalities.
3. Women who have experienced previously failed embryo implantation
4. Women diagnosed with unexplained infertility.

METHODOLOGY

1. The first step is an embryo biopsy.
2. In both forms of testing, the biopsy is at the blastocyst (day five or day 6 of embryo culture) stage of development.
3. TE allows the placenta and inner cell mass (ICM) to develop, which later develops into the baby.
4. Results are usually available within 10 -14 days following the biopsy.

Preimplantation genetic testing can be of three types: PGT-A, PGT-M, and PGT-SR

PGT-A stands for preimplantation genetic testing for detecting aneuploidy

• PGT-A analyses embryo cells to determine if there is an average number of chromosomes.
• Trisomy of chromosome pairs can sometimes result in a live birth, Down syndrome, also called trisomy 21 (an extra chromosome in average pair # 21), Turner syndrome (trisomy 18) and Patau syndrome (trisomy 13).

PGT-M stands for preimplantation genetic testing for the detection of monogenic gene disorders

• PGT-M analyzes a child being born with a genetic mutation.
• It can also cause an inherited genetic mutation, such as the BRCA1 and BRCA2 mutations, significantly increasing a woman’s risk of breast and ovarian cancer.

PGT-M examines common disorders, including:

1. Huntington’s disease
2. Sickle cell anaemia
3. Muscular dystrophy
4. Cystic fibrosis
5. BRCA1 & BRCA2 mutations
6. Fragile-X syndrome
7. Tay-Sachs disease

PGT-SR stands for preimplantation testing for structural rearrangements

Preimplantation genetic testing-structural rearrangements are used to test embryos at risk for chromosome gains and losses related to parental structural chromosomal abnormalities (e.g. translocations, inversions, deletions, and insertions).

LIMITATIONS

• Patients and healthcare providers should know that a negative preimplantation genetic test result does not guarantee a newborn without congenital abnormalities.
• Furthermore, experienced laboratory personnel in IVF and genetics are essential for a patient’s success.

BENEFITS

• Euploid embryo transfer results in the highest pregnancy and live birth rates, reducing miscarriage risk independent of maternal age.
• PGT-M and PGT-SR exclude the affected embryos, preventing the disorder’s genetic transmission to the offspring.

CONCLUSION: PGT is a primary diagnostic tool to prevent any known genetic disorder transmission. It also helps in populations at high risk of having babies with specific genetic aberrations.