PGD/PGT Genetic Screening: Which Diseases Does It Help Prevent for a Healthy Baby?

Examining an embryo’s genetic makeup before it is transferred to the uterus in IVF treatment is no longer science fiction; it is part of everyday clinical practice. So what exactly does this genetic screening, known as PGD/PGT, prevent, which diseases can it detect, and what are its limitations? As GynoLife IVF, we explain this technology, applied in our laboratory in Nicosia, within its scientific facts and legal framework.

What Is PGD/PGT, and When Is It Recommended?

PGT (Preimplantation Genetic Testing) is the genetic examination of a fertilized embryo, usually at the blastocyst stage (day 5-6), through a biopsy of a few cells, before it is transferred to the uterus in IVF treatment. The older term PGD (Preimplantation Genetic Diagnosis) is used today mainly for screening single-gene diseases, while PGT serves as an umbrella term divided into three subcategories: PGT-A, PGT-M, and PGT-SR.

This screening offers particular benefit in the following situations:

• Advanced maternal age (35 and older)
• Recurrent implantation failure or a history of miscarriage
• Known carrier status for a hereditary disease in one partner or in the family
• A previous pregnancy with a chromosomal anomaly
• A balanced chromosomal translocation in one of the parents

PGT-A, PGT-M, PGT-SR: Three Tests, Three Different Purposes

PGT-A (Aneuploidy Screening)

PGT-A examines the number of the embryo’s 23 pairs of chromosomes. The goal is to detect, before transfer, conditions caused by an extra chromosome, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), as well as chromosomal imbalances that result in miscarriage. Selecting chromosomally normal (euploid) embryos can increase implantation rates and reduce the risk of miscarriage; this is an approach particularly favored in patients of advanced age.

PGT-M (Single-Gene Disease Screening)

PGT-M is applied for hereditary diseases known in the family that result from a mutation in a single gene. This test only works in a targeted way once the specific mutation carried by the parents has been identified beforehand. Some of the diseases that can be screened include:

• Thalassemia (Mediterranean anemia): An indication we frequently encounter in our clinical practice, since carrier frequency is high in Cyprus and the surrounding region
• Cystic fibrosis: Caused by mutations in the CFTR gene
• Spinal muscular atrophy (SMA): Caused by mutation in the SMN1 gene
• Sickle cell anemia
• Huntington’s disease
• Hereditary cancer predisposition linked to BRCA1/BRCA2 and similar late-onset conditions (evaluated together with ethical counseling)

PGT-SR (Structural Rearrangements)

PGT-SR is used when one of the parents has a structural chromosomal rearrangement, such as a balanced translocation or inversion. This condition usually does not affect the parent, but it can lead to an unbalanced chromosome distribution in the embryo and result in recurrent miscarriage. PGT-SR helps identify embryos that do not carry this kind of imbalance.

What Happens in the Laboratory? NGS Technology

The small sample of cells taken from a blastocyst-stage embryo via biopsy is now most commonly analyzed using Next Generation Sequencing (NGS). Compared with earlier-generation techniques (such as FISH), NGS can assess chromosome number and structure at a much higher resolution, and can even detect certain levels of mosaicism. During the biopsy, the embryo is frozen (vitrified) while the laboratory result is awaited; once the result is available, the embryo found to be genetically suitable for transfer is placed in the uterus via a frozen embryo transfer (FET) protocol. This “biopsy-freeze-wait-transfer” approach allows both the genetic result to be assessed reliably and the uterine lining to be optimally prepared, compared with a fresh transfer.

A brief note on mosaicism: some embryos may contain a mix of cells with normal and abnormal chromosomal structure. These embryos are classified as “mosaic” and require a more nuanced counseling process than embryos that are entirely normal or entirely abnormal. The decision about transferring mosaic embryos is made by evaluating the patient’s history, the number of embryos available, and the opinion of a genetic counselor together.

What Doesn’t PGD/PGT Guarantee?

Scientific honesty matters here: PGT does not rule out any disease other than the specific chromosomal or genetic conditions being screened for, and it does not guarantee a “100% healthy baby.” The test is based on a limited number of cells taken from the embryo; in rare cases, conditions such as mosaicism (different genetic makeup in different cells of the embryo) can complicate the interpretation of the results. In addition, the test cannot predict environmental or multifactorial diseases that may appear after birth. For this reason, every PGT process should be planned with an experienced genetic counselor, based on a personalized risk assessment for the patient.

Important: Use for Sex Selection Is Not Legal

PGT technology can also reveal the sex of the embryo; however, using this solely for family preference “sex selection,” outside of a medical indication, is not accepted in Cyprus, as in many other countries, and is not permitted under the ethical and legal framework GynoLife IVF operates under. PGT-M can produce a sex-related result only when there is a medical justification, such as the risk of an X-linked hereditary disease; this should not be confused with sex selection. Our clinic conducts all genetic screening processes solely based on medical indication and patient health priorities.

How Does the Process Work at GynoLife IVF?

Before treatment, our genetic counselors review family history and any carrier screening results. When the embryos obtained during the IVF process reach the blastocyst stage, our experienced embryologists perform a safe biopsy procedure, and the samples are sent to accredited genetic laboratories. Based on the results, the embryo(s) found to be genetically suitable for transfer are selected through joint evaluation. Our patients are kept informed at every stage of the process and included in the decision-making.

Frequently Asked Questions

Does PGT/PGD harm the embryo?

According to current evidence, blastocyst biopsy performed by experienced hands does not meaningfully affect the embryo’s developmental potential. Still, as with any medical procedure, there is a very small degree of risk, and this is discussed openly with the patient.

Is PGT-A recommended for everyone?

No. The cost-benefit balance varies depending on the patient’s age, history, and number of embryos, so the decision should be individualized.

How long does it take to get test results?

Depending on the laboratory and the test, this usually ranges from a few days to one or two weeks; this time frame can affect transfer planning.

I don’t know if I’m a carrier — can PGT-M still be done?

PGT-M requires first knowing which mutation is being looked for in the family; for this reason, the process usually starts with carrier screening.

If the result comes back mosaic, can the embryo still be transferred?

In some cases, yes, but this decision is evaluated individually, together with a genetic counselor, based on the embryo’s degree of mosaicism, the patient’s history, and whether other embryos are available.

Does doing PGT-A guarantee my chance of pregnancy?

No. PGT-A contributes to the selection process by identifying a chromosomally suitable embryo, but there are many other factors that affect implantation success, such as the uterine environment and embryo quality. No medical test can guarantee pregnancy or a healthy birth.

You can contact the GynoLife IVF Cyprus team to learn more about genetic screening options and how your treatment can be personally planned for you. Let’s discuss your situation together with a free preliminary assessment and map out the roadmap that is right for you.