Understanding Preimplantation Genetic Testing for IVF Success

Preimplantation Genetic Testing (PGT) also known as preimplantation genetic diagnosis (PGD) plays an essential role in IVF today, helping identify embryos with the best potential for a healthy pregnancy. As demand for personalised, precision-based IVF grows, clinicians must stay informed about the three main types of PGT namely PGT-A, PGT-M, and PGT-SR and how they can be effectively integrated into clinical practice.

MedGenome offers a comprehensive portfolio of PGT services backed by high-throughput genomics, clinical-grade reporting, and genetic counselling support, enabling specialists to make data-driven embryo selection decisions with confidence.

What Is Preimplantation Genetic Testing?

PGT includes a group of genetic tests performed on embryos before transfer. These tests are designed to improve the selection of embryos by identifying chromosomal or genetic abnormalities that may affect implantation or fetal development.¹

PGT is typically performed at the blastocyst stage, using cells from the trophectoderm, which is the outer layer of cells in a blastocyst that later forms the placenta. This method avoids disturbing the inner cell mass that will form the fetus. However, mosaicism (a condition where an embryo has both normal and abnormal cells) can present a challenge, since the trophectoderm may not perfectly represent the entire embryo’s genetic profile. ¹ ² ³

Types of Preimplantation Genetic Testing

There are three types of PGT, each with a distinct purpose:

PGT-A (for Aneuploidies)
PGT-M (for Monogenic disorders)
PGT-SR (for Structural Rearrangements)

1. PGT-A (Testing for Aneuploidy):

PGT-A screens for whole chromosome abnormalities, including all 22 autosomes and sex chromosomes. It is particularly helpful in:

Patients of advanced maternal age (35+)
Couples with recurrent miscarriages
Previous IVF failure
Single embryo transfer planning
Couples with a history of pregnancy affected by aneuploidy ¹ ² ⁴

Conditions this test can detect:

Turner syndrome
Klinefelter syndrome
Down syndrome
Edwards syndrome
Patau syndrome
Other trisomies and monosomies

MedGenome uses Next Generation Sequencing (NGS) platforms to ensure full chromosomal screening with enhanced sensitivity for detecting anomalies such as mosaicism. While current guidance does not recommend PGT-A universally, it may benefit select patients, especially when used alongside strong genetic counselling and embryo scoring. ² ⁴

2. PGT-M (Testing for Monogenic Disorders):

PGT-M is used when one or both biological parents are carriers of a specific genetic disorder caused by mutations in a single gene (monogenic) ⁵. It is recommended for:

Couples with a known family history of a single-gene disorder
Consanguineous couples who are identified to be carriers
Carrier couples identified through expanded carrier screening ²

Conditions this test can detect:

Cystic fibrosis
Thalassemia
Tay-Sachs disease
Huntington’s disease
BRCA 1 & 2 mutations
Sickle cell anemia
Muscular dystrophy
Fragile-X syndrome

PGT-M requires prior customisation of the testing process for each family, including DNA workup called Pre-PGT of the parents and, sometimes, other family members. It is targeted and highly specific. ²

3. PGT-SR (Testing for Structural Chromosomal Rearrangements):

PGT-SR is used when one of the parents carries a balanced chromosomal translocation or inversion, which can lead to the production of embryos with unbalanced genetic material. How is it different from PGT-A? While PGT-A screens for random aneuploidies, PGT-SR focuses on chromosomal rearrangements that increase the risk of miscarriage or serious genetic conditions.² ⁶

It cannot distinguish between normal embryos and those with balanced translocations, and it cannot detect some risks, such as uniparental disomy. Confirmation with prenatal diagnostic testing is recommended. ²

It is usually recommended for:

Couples where one or both partners have a known chromosomal rearrangement (e.g. Robertsonian or reciprocal translocation)
Couples with a history of recurrent miscarriages
Parents who previously had a child with an unbalanced chromosomal condition ² ⁶

This test cannot distinguish between normal embryos and those with balanced translocations, and it cannot detect some risks, such as uniparental disomy. Confirmation with prenatal diagnostic testing is recommended. ²

Limitations of Preimplantation Genetic Testing

Despite its benefits, PGT has limitations ²:

It may miss de novo mutations, microdeletions, or imprinting disorders
Results can rarely be false positives or false negatives
Mosaicism complicates interpretation

Prenatal diagnostic testing should still be offered to all patients after PGT.

Do Patients Still Need Prenatal Testing After PGT?

Yes. Even after PGT, prenatal genetic screening or diagnostic testing should be offered. This is because PGT cannot detect every possible genetic issue.²

Prenatal testing options include:

Chorionic villus sampling (CVS)
Amniocentesis

Shared decision-making with patients is essential. For those who decline diagnostic testing, it is important to discuss the limitations of screening.

The Role of IVF Specialists

As IVF specialists, understanding Preimplantation Genetic Testing enables you to ²:

Recommend the right tests based on each patient’s genetic background
Work closely with genetic counsellors
Guide patients with realistic expectations about success rates and outcomes
Explain mosaic embryo results and support informed transfer decisions

In Conclusion

Preimplantation Genetic Testing (PGT), whether PGT-A, PGT-M or PGT-SR, is a valuable part of modern IVF. As technology improves, we can offer safer and more informed reproductive choices. IVF specialist play a key role in using these genetic tools to guide patient care. Understanding the different types of PGT is important for achieving the best outcomes.

By selecting the right test for the right patient at the right time, you give hopeful parents the knowledge, confidence, and improved chance of a healthy pregnancy.

FAQ’s

1. What is the difference between PGT-A, PGT-M, and PGT-SR?

PGT-A screens for chromosome number abnormalities (aneuploidy).
PGT-M tests for specific single-gene disorders.
PGT-SR detects losses and gains typically seen when parents are translocation carriers.

2. Can PGT detect all genetic disorders?

No. PGT cannot detect every condition, especially de novo mutations, microdeletions, or imprinting disorders. Some rare conditions may go undetected. PGT-M is meant to detect only a specific condition.

3. What is mosaicism, and why does it matter?

Mosaicism means the embryo has a mix of genetically normal and abnormal cells. Its presence can lower success rates or increase uncertainty. In some cases, mosaic embryos may still lead to healthy live births.

4. Should patients still get prenatal testing if they had PGT?

Yes. PGT is not a substitute for prenatal screening or diagnostic tests. All pregnant patients should be offered standard prenatal care.

5. Is PGT-A recommended for everyone undergoing IVF?

Not at this time. According to current guidance, there is not enough evidence to support routine PGT-A for all IVF patients. It may be more useful in selected cases.