PGT-A (Preimplantation Genetic Testing for Aneuploidy)

PGT-A (Preimplantation Genetic Testing for Aneuploidy) is primarily used in in vitro fertilization (IVF) treatments to assess whether embryos have numerical chromosomal abnormalities (aneuploidy). This helps clinicians select embryos with higher developmental potential for transfer.

Chromosomal aneuploidy is one of the major causes of implantation failure, early miscarriage, and IVF failure. Its incidence increases significantly with advancing maternal age.

Association Between Aneuploid Embryos and Reproductive Outcomes

A normal human embryo should contain 23 pairs, for a total of 46 chromosomes.

If an embryo has too many or too few chromosomes, it may result in:

· Arrested embryonic development

· Recurrent implantation failure

· Early or mid-term miscarriage

· Chromosome-related disorders (such as triploidy, monosomy, etc.)

Studies have shown that even morphologically good-quality blastocysts may still carry chromosomal abnormalities. Therefore, embryo appearance alone is insufficient to accurately reflect chromosomal status.

What is going through during PGT-A?

• Blastocyst Culture
Embryos are cultured to the blastocyst stage on Day 5–6. 

• Trophectoderm Biopsy
A small number of cells are removed from the outer layer (trophectoderm) of the blastocyst by an experienced embryologist.
This region will later develop into the placenta and does not involve the inner cell mass (ICM), resulting in minimal impact on embryo development.

• Embryo Cryopreservation
After biopsy, the embryo is immediately vitrified (rapid freezing) while waiting for the test results.

• Chromosomal Analysis
High-resolution technologies, such as next-generation sequencing (NGS), are used to analyze the numerical status of all 23 pairs of chromosomes.

Clinical Indications for PGT-A

PGT-A is an assisted reproductive technology and is particularly recommended for following situations:

· Maternal age ≥35 years

· Recurrent miscarriage (≥2 losses)

· Repeated IVF/ICSI implantation failure

· Previous pregnancy or childbirth affected by chromosomal abnormalities

· Planned single embryo transfer (SET) to reduce the risk of multiple pregnancy

· Adequate number of embryos available for selection

Clinical Advantages of PGT-A

· Improved implantation rate

· Reduced clinical miscarriage rate

· Increases the success rate of single embryo transfer

· Lower risks associated with multiple pregnancies

· Shortened time to achieve pregnancy

PGT-A serves as an important tool to improve both the efficiency and safety of IVF treatment for selected population.

Limitations and Considerations of PGT-A

· PGT-A cannot guarantee pregnancy or live birth

· It does not detect all genetic diseases (only numerical chromosomal abnormalities)

· Mosaicism results may occur and require professional interpretation by physicians

· Pregnancy outcomes still depend on uterine conditions, embryo quality, and maternal factors

Therefore, PGT-A should be regarded as a decision-support tool rather than an absolute predictor.

Differences Between PGT-A, PGT-M, and PGT-SR

Preimplantation Genetic Testing (PGT) refers to a group of genetic testing technologies performed during IVF treatment before embryo transfer.

Based on different testing purposes, PGT is categorized into PGT-A, PGT-M, and PGT-SR, each with distinct indications and testing purposes.

PGT-M: Monogenic Disorder Testing

PGT-M is used to determine whether embryos carry or are affected by specific known single-gene hereditary disorders.

Common Applicable Diseases

· Thalassemia

· Spinal Muscular Atrophy (SMA)

· Cystic Fibrosis (CF)

· Hemophilia

· Other hereditary diseases with clearly identified pathogenic genes

Clinical Characteristics

· Parental genetic mutations must be identified in advance

· Customized test design is required for each family

· Prevents transmission of specific genetic diseases to the next generation

PGT-SR: Structural Rearrangement Testing

PGT-SR is mainly used for couples with chromosomal structural abnormalities, such as:

· Balanced chromosomal translocations (reciprocal / Robertsonian)

· Chromosomal inversions

Clinical Applications

· Differentiation between balanced and unbalanced embryos

· Reduced risk of miscarriage and abnormal embryonic development

· Improved accuracy in selecting transferable embryos

Suitable Candidates

· Individuals diagnosed as carriers of chromosomal structural abnormalities

· Patients with unexplained recurrent miscarriage