PGS/PGT Explained: Genetic Testing of Embryos Before Transfer

One of the most powerful advances in modern IVF treatment is the ability to check an embryo's genetics before it is transferred. This is known as preimplantation genetic testing — you may have heard it called PGS or PGT — and for many couples it can mean fewer miscarriages, a higher chance of pregnancy per transfer, and the reassurance of transferring a healthy embryo.

But the terminology is confusing, and not everyone needs it. In this guide, the specialists at Myra IVF Centre in Kenya, led by Dr. Sarita Sukhija, explain exactly what PGS/PGT is, the different types, how it works, who benefits — and its honest limitations.

PGS vs PGT: What's the Difference?

The two terms cause a lot of confusion, so let's clear it up:

• PGS (Preimplantation Genetic Screening) is the older name for screening embryos for the correct number of chromosomes.
• PGT (Preimplantation Genetic Testing) is the current umbrella term for all embryo genetic testing. What used to be called PGS is now known as PGT-A.

In other words, PGS hasn't disappeared — it has simply been renamed and now sits within the broader PGT family.

The Three Types of PGT

There are three distinct tests, each answering a different question about the embryo:

Test	What it checks	Best for
PGT-A (formerly PGS)	The number of chromosomes (aneuploidy) — a missing or extra chromosome, e.g. the extra chromosome in Down syndrome	Advanced maternal age, recurrent miscarriage, repeated IVF failure
PGT-M (monogenic)	A specific single-gene disorder, e.g. sickle cell disease, thalassaemia or cystic fibrosis	Couples who are known carriers of an inherited genetic condition
PGT-SR (structural)	Unbalanced chromosome rearrangements such as translocations	Parents who carry a known structural chromosome rearrangement

How Genetic Testing of Embryos Works: Step by Step

PGT is woven into a normal IVF cycle. Here is what actually happens:

• Step 1 — Egg retrieval and fertilisation: Eggs are collected during egg retrieval and fertilised, almost always using ICSI to avoid stray sperm affecting the genetic result.
• Step 2 — Blastocyst culture: Embryos are grown to the blastocyst stage (day 5 or 6), when they are robust enough for biopsy.
• Step 3 — Embryo biopsy: An embryologist gently removes a few cells from the trophectoderm — the part of the embryo that later becomes the placenta, not the baby.
• Step 4 — Freezing: The biopsied embryos are frozen by vitrification while the cells are analysed. (This is why PGT cycles use a frozen embryo transfer.)
• Step 5 — Genetic analysis: The sample is tested in a specialised genetics laboratory, usually with next-generation sequencing.
• Step 6 — Transfer of a healthy embryo: Once results are ready, a single healthy embryo is thawed and transferred in a later, carefully prepared cycle.

Who Should Consider PGT?

PGT is not necessary for every patient, but it can be especially valuable for:

• Women of advanced maternal age (usually 35+), as the chance of chromosomal abnormalities in eggs rises with age.
• Couples with recurrent miscarriage, many of which are caused by chromosomal errors.
• Those with repeated IVF failure or failed implantation despite good-quality embryos.
• Known carriers of a genetic condition such as sickle cell disease or thalassaemia (PGT-M).
• Carriers of a chromosomal rearrangement such as a translocation (PGT-SR).
• Couples choosing single embryo transfer to reduce the risk of twins while keeping success rates high.

The Benefits of PGT

• Higher implantation rate per transfer — selecting a chromosomally normal embryo improves the chance it will implant.
• Lower miscarriage risk — most early miscarriages are linked to chromosomal errors that PGT-A can detect.
• Fewer failed cycles and, often, a shorter time to a healthy pregnancy.
• Safer single embryo transfer — reducing multiple pregnancies without lowering success.
• Prevention of specific inherited diseases with PGT-M and PGT-SR.

Honest Limitations to Understand

PGT is powerful, but it is not a magic wand. It's important to know the boundaries:

• It is not 100% accurate, and some embryos show "mosaic" results that can be harder to interpret.
• It does not test for every condition — only the specific chromosomes or genes assessed.
• It does not replace routine pregnancy screening and antenatal care.
• It requires biopsy and freezing, adding steps and cost to the IVF cycle.
• The benefit is smaller for younger women who already produce many healthy embryos.

PGT and Family Balancing

Because PGT-A examines all of an embryo's chromosomes, it also reveals the sex chromosomes. Where it is legally and ethically permitted, this allows family balancing. At Myra IVF Centre, this is offered through our dedicated PGS / family balancing programme and gender selection service, always within applicable regulations and after appropriate counselling.

PGT at Myra IVF Centre, Kenya

At Myra IVF Centre, genetic testing is delivered as part of a carefully coordinated IVF pathway:

• Expert embryo biopsy performed at the blastocyst stage in our ISO 9001 certified laboratory.
• Advanced genetic analysis covering PGT-A, PGT-M and PGT-SR as clinically indicated.
• Freeze-all and frozen embryo transfer protocols to give the healthiest embryo the best environment.
• Genetic counselling and clear guidance so you can make an informed choice.
• A dedicated PGS / family balancing facility for eligible couples.
• Three convenient locations — Nairobi, Mombasa and Kisumu.

With over 15 years of experience and a 79% overall IVF success rate, Myra IVF Centre has helped thousands of couples across Kenya and East Africa build healthy families.

Conclusion

PGS/PGT lets your fertility team look beyond how an embryo looks and check its genetic health before transfer. For the right patients — older women, those with recurrent miscarriage or IVF failure, and carriers of genetic conditions — it can meaningfully improve the chance of a healthy pregnancy and reduce heartbreak along the way. It is not needed by everyone, and it is not a guarantee, but used wisely it is one of the most valuable tools in modern IVF.

If you'd like to know whether genetic testing is right for your embryos, speak with our fertility specialists at Myra IVF Centre — we'll explain your options clearly and honestly.

Book a consultation today. Contact us at +254 786656236 or drsarita2007@gmail.com.