PGT-A (Preimplantation Genetic Testing for Aneuploidy)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated July 27, 2026

PGT-A (Preimplantation Genetic Testing for Aneuploidy) is a laboratory procedure performed on an embryo biopsy during IVF to screen for chromosomal aneuploidy before transfer. It was formerly called PGS (Preimplantation Genetic Screening), and that older term is still widely used in patient-facing materials and online searches.¹ A trophectoderm biopsy removes cells from the blastocyst; next-generation sequencing (and, historically, array comparative genomic hybridization, now largely superseded) determines chromosomal copy number.² Embryos the analysis designates as euploid (chromosomally normal) are selected for transfer; aneuploid embryos are typically discarded or frozen and not transferred.³

PGT-A is marketed as a tool to improve IVF success rates by transferring only chromosomally screened embryos.⁴ The evidence for routine use in good-prognosis patients does not support that claim.⁵ A multicenter randomized clinical trial (the STAR trial, Fertil Steril 2019) assigned 661 good-prognosis patients to either PGT-A-based embryo selection or morphology-based selection. By intention-to-treat analysis, ongoing pregnancy rates at 20 weeks were 41.8% in the PGT-A group (138/330) versus 43.5% in the morphology group (144/331). The difference was not statistically significant.⁴ Subgroup analyses suggested possible differences by age, but these findings were post hoc, restricted to women with sufficient embryos to biopsy, and did not reach significance on the primary intention-to-treat analysis. Even where a per-transfer or subgroup advantage appears, one proposed explanation is that PGT-A speeds identification of a viable embryo from an existing set rather than increasing the number of healthy embryos in that set; this remains a hypothesis about why per-transfer gains may not translate to cumulative outcomes.⁴

One proposed reason cumulative outcomes may not improve is that biopsy and discard reduce the pool of embryos available for subsequent transfers, so a per-transfer gain need not translate into more children per patient.⁶ Whether routine PGT-A raises cumulative live birth per egg retrieval remains contested; in the largest datasets to date, good-prognosis patients have not demonstrated a cumulative gain.⁵ The biopsy process also classifies some embryos as mosaic: carrying both normal and abnormal cells.⁷ Some mosaic embryos have gone on to healthy live births, though outcomes vary with the chromosome involved and the degree of mosaicism.⁸ That variability is why discarding a mosaic embryo on a single trophectoderm biopsy result represents a decision with clinical and ethical weight that a per-transfer success metric alone does not capture.⁹

PGT-A screens embryos that IVF has already created outside the body. It sorts them by chromosomal status to influence which one is transferred. That sorting step does not change the biology that produced the embryos: egg quality, age-related chromosomal error rates, and the treatable conditions behind aneuploidy and recurrent pregnancy loss remain exactly as they were.⁵ The couple carries the same unresolved reproductive dysfunction into the next cycle.¹⁰

PGT-A is sometimes confused with PGT-M (Preimplantation Genetic Testing for Monogenic Disorders). The two address different questions. PGT-A screens for chromosomal copy-number errors across the whole genome, such as extra or missing chromosomes. PGT-M screens for a specific inherited single-gene disorder, such as cystic fibrosis or sickle cell disease, when one or both partners carry a known genetic variant.¹¹ Both require IVF and embryo biopsy; from an RRM perspective, PGT-A and PGT-M screen embryos for chromosomal or monogenic variants but leave the underlying cause of natural conception failure unaddressed and undiagnosed.¹⁰

PGT-A is specific to IVF. It applies only when embryos are created outside the body and biopsied before transfer. Natural conception, which RRM supports and facilitates, does not involve embryo creation outside the body, embryo biopsy, or chromosomal selection.¹⁰ The question PGT-A is designed to answer does not arise in restorative care.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.