IVF & assisted reproduction
PGT-A preimplantation genetic testing: indications and accuracy
By Dr. Suresh Kattera · 17 min read · Published
What is PGT-A (Formerly PGS)?
Under standard embryological evaluation, blastocysts are graded morphologically (e.g., 4AA, 3BB) based purely on visual appearance. However, multiple clinical studies confirm that up to 40% of visually "flawless" 4AA blastocysts harbor lethal chromosomal abnormalities (aneuploidies) that make successful live birth impossible.
PGT-A directly evaluates chromosome count. A normal human cell contains 46 chromosomes (23 pairs):
- Euploid: Normal complement of 46 chromosomes (22 autosome pairs + XX or XY sex chromosomes).
- Aneuploid: Missing a chromosome (monosomy) or possessing an extra chromosome (trisomy, such as Down syndrome, Edwards syndrome, or Patau syndrome).
- Mosaic: An embryo containing both euploid and aneuploid cell lines in the biopsied sample.
The Biopsy Technique: Protecting the Inner Cell Mass
A primary fear among patients is whether genetic testing damages the future baby:
- Trophectoderm Only: The biopsy samples only 5 to 8 cells from the trophectoderm layer, which exclusively forms the placenta and gestational sac.
- Untouched Inner Cell Mass: The inner cell mass that develops into the fetus remains completely undisturbed.
- Laser-Assisted Precision: A focused infrared diode laser cleanly separates cellular junctions in milliseconds with zero thermal injury to surrounding cells.
Clinical Indications: Who Benefits Most from PGT-A?
- Advanced Maternal Age (≥ 35 Years): Where baseline aneuploidy rates exceed 40% to 70%.
- Recurrent Implantation Failure (RIF): History of 2 or more failed high-grade blastocyst transfers.
- Recurrent Pregnancy Loss (RPL): Two or more unexplained early miscarriages.
- Severe Male Factor Infertility: High Sperm DNA Fragmentation Index (>30%) or severe oligoasthenoteratozoospermia.
- Single Embryo Transfer Prioritization: When a patient desires the fastest route to pregnancy with zero twin risk.
Frequently asked questions
PGT-A screens for whole or large segmental numerical chromosome abnormalities (aneuploidies), which cause the vast majority of failed transfers and first-trimester miscarriages. It does not screen for single-gene mutations (such as cystic fibrosis or sickle cell disease, which require PGT-M) or polygenic developmental conditions.
Yes. Recent international guidelines from the Preimplantation Genetic Diagnosis International Society (PGDIS) indicate that low-level mosaic embryos (<50% abnormal cells) possess remarkable self-correction mechanisms and can achieve successful live births when prioritized correctly.