cutting edgetechnology

PGT-A

PGT-A Chromosome Screening

Additional Chromosome Information Before Transfer

An embryo that appears to be developing well does not necessarily have a normal chromosome number.

Chromosome number abnormalities generally become more common with increasing maternal age. Affected embryos may fail to implant, miscarry, or be associated with certain chromosome conditions.

Preimplantation genetic testing for aneuploidy (PGT-A) analyzes a small sample of embryo cells before transfer to assess chromosome number and inform embryo selection and treatment planning.

PGT-A is a chromosome screening technique, not a comprehensive test for every genetic condition. It cannot guarantee pregnancy or a healthy child. The source article refers to ASRM guidance that does not recommend routine PGT-A for every IVF patient.

How Is PGT-A Performed?

PGT-A is performed as part of IVF. It cannot be completed through a blood test alone.

STEP 1 | Ovarian Stimulation and Egg Retrieval

A stimulation protocol is selected according to ovarian function, followed by retrieval at the appropriate time.

STEP 2 | Fertilization

Mature eggs are fertilized in the embryology laboratory and monitored as they develop.

STEP 3 | Culture to the Blastocyst Stage

Embryos are generally cultured to the blastocyst stage.

Only embryos that reach a stage suitable for biopsy can be sampled. Not every fertilized egg will develop sufficiently to undergo testing.

STEP 4 | Blastocyst Biopsy

An embryologist removes a small number of cells from the outer trophectoderm layer.

These cells mainly contribute to placental tissues. The sample is not taken directly from the inner cell mass that develops into the fetus. Trophectoderm biopsy is a commonly used sampling approach.

STEP 5 | Embryo Vitrification

After biopsy, embryos are usually vitrified and stored while results are pending.

STEP 6 | Chromosome Analysis

The sampled cells are sent to a testing laboratory. Techniques such as next-generation sequencing (NGS) are commonly used to assess chromosome findings.

STEP 7 | Transfer Planning

Your doctor reviews the report alongside embryo findings, endometrial conditions, and reproductive plans to discuss the next steps.

When Might PGT-A Be Discussed?

• Older reproductive age
• A history of recurrent miscarriage
• A previous pregnancy affected by a chromosome abnormality
• Repeated unsuccessful embryo transfers
• Several available blastocysts and a wish for additional selection information
• Other circumstances assessed by fertility and genetics professionals

These circumstances do not automatically mean PGT-A is necessary.

PGT-A has not been shown to improve cumulative live birth rates for every IVF patient. It may help avoid transfer of embryos with detected chromosome abnormalities, but its clinical value depends on age, available blastocyst number, and individual treatment circumstances.

Is Prenatal Testing Still Needed After PGT-A?

Yes.

PGT-A is performed before embryo transfer and does not replace standard prenatal care or prenatal genetic assessment.

After pregnancy is established, appropriate prenatal screening or diagnostic options should still be discussed according to age, medical history, and clinical advice.

Time-Lapse Embryo Culture System

Time-Lapse Embryo Culture

Recording Each Stage of Embryo Development

A fertilized egg undergoes repeated cell divisions and developmental changes before becoming a blastocyst suitable for transfer.

Conventional assessment involves observations at scheduled times to examine cell number, appearance, and developmental stage. A time-lapse system integrates imaging into the incubator to record embryos at regular intervals.

Embryologists can review not only the current appearance but also the sequence and timing of development from fertilization to blastocyst formation.

What Happens During Embryo Culture?

After fertilization, development typically progresses through stages such as:

Fertilized egg → 2-cell stage → 4-cell stage → 8-cell stage → Morula → Blastocyst.

Not every embryo develops at exactly the same pace.

Embryologists consider morphology, division patterns, and development timing when planning further culture, freezing, or transfer.

How Does It Differ from Conventional Culture?

Conventional Culture

Embryos are maintained in a suitable culture environment and assessed by embryologists at scheduled times.

This is an established clinical approach and remains a standard method of embryo culture.

Time-Lapse Culture

Embryos develop under controlled temperature, gas concentrations, and culture conditions while the system captures images automatically.

Embryologists can review images without removing the culture dish solely to obtain each observation.

Regardless of the system, stable temperature, pH, gas concentrations, and osmolality remain central to embryo culture. Minimizing environmental fluctuations and monitoring culture conditions are important laboratory priorities.

Can Time-Lapse Imaging Determine Whether Chromosomes Are Normal?

No.

Although certain developmental patterns may be associated with chromosome abnormalities, images alone cannot reliably establish whether an embryo is euploid.

Time-lapse imaging does not replace PGT-A for obtaining chromosome screening information.

Time-lapse imaging: observes development and morphology.

PGT-A: analyzes chromosome number in sampled cells.

Their purposes are different.

When May Time-Lapse Culture Be Used?

Depending on the center’s equipment and protocols, it may be used for:

1. In vitro fertilization (IVF)
2. Intracytoplasmic sperm injection (ICSI)
3. Blastocyst culture
4. Treatment requiring detailed developmental observation
5. Other circumstances assessed by the clinical and embryology teams

Its use depends on laboratory systems and treatment planning. It is not an essential requirement for successful embryo culture.

Embryo Cryopreservation

Embryo Freezing & Warming

From Vitrification to Warming and Embryo Transfer

Not all embryos obtained during IVF are transferred in the same cycle.

Freezing may be appropriate when several suitable embryos are available, genetic testing results are pending, the endometrium is unsuitable for immediate transfer, or the treatment plan favors a later transfer.

Vitrification is widely used for egg and embryo cryopreservation and is an established laboratory approach for preserving reproductive cells and embryos.

When Might Embryo Freezing Be Recommended?

Several Suitable Embryos Are Available

Embryos do not all need to be transferred at once. Remaining suitable embryos can be preserved according to the treatment plan.

Preimplantation Genetic Testing Is Planned

After blastocyst biopsy, embryos are usually frozen while test results are pending. Transfer is then planned according to the report and clinical findings.

The Current Cycle Is Unsuitable for Transfer

The hormonal environment, endometrium, or general health after stimulation may make a later transfer more appropriate.

Reducing Certain Treatment Risks

For some patients with a strong ovarian response or increased OHSS risk, a freeze-all strategy may be recommended, with transfer planned after recovery.

Future Family Planning

Remaining suitable embryos may be stored according to applicable law, medical assessment, consent, and reproductive plans.

Embryo Cryopreservation

Does Longer Storage Mean Lower Embryo Quality?

Cryopreservation aims to maintain embryos in a stable state at very low temperatures.

Important factors affecting later treatment outcomes include:

• Age at egg retrieval
• Embryo quality before freezing
• Developmental stage
• Freezing and warming techniques
• Survival after warming
• The endometrial environment
• Overall maternal health

The number of years in storage alone cannot determine whether a future pregnancy will succeed.

What If an Embryo Does Not Survive Warming?

Although cryosurvival has improved substantially, no freezing and warming procedure can guarantee 100% survival.

If the intended embryo is unsuitable for transfer after warming, the clinical and embryology teams will discuss whether another embryo can be warmed or the treatment plan should be revised, according to remaining embryos, prior consent, and individual circumstances.