Preimplantation genetic testing (PGT): which version is right, when, and why

Preimplantation genetic testing (PGT) screens embryos created during IVF before transfer. There are three different versions of PGT, each answering a different clinical question. Which one – if any – belongs in your cycle depends on your diagnosis, not on a marketing list.

PGT-A: testing for chromosomal number

PGT-A looks for embryos with the right number of chromosomes (euploid) versus extra or missing ones (aneuploid). It is most useful for women over 38, where aneuploidy rates rise sharply. In good labs, transferring a euploid embryo gives ongoing pregnancy rates of 50 to 60 percent per transfer regardless of maternal age – a meaningful improvement when you are working with limited embryos.

The harder honest answer: in younger patients with normal-looking embryos, the largest randomised trials have not shown that PGT-A improves cumulative live-birth rate compared to transferring untested embryos in sequence. The biopsy adds a small risk, and embryos with mosaic results sit in a frustrating grey zone.

PGT-M: testing for a specific known disease

PGT-M (formerly PGD) is performed when one or both parents carry a known single-gene condition – cystic fibrosis, sickle cell, beta-thalassemia, BRCA1/2, Huntington’s. The lab develops a custom assay for that family’s specific variant and identifies which embryos are unaffected. This is one of the clearest indications for PGT and is genuinely transformative for affected families.

PGT-SR: testing for chromosomal rearrangements

PGT-SR is used when one parent carries a balanced chromosomal rearrangement (translocation, inversion). The carrier parent is usually unaffected but produces a high proportion of unbalanced embryos that miscarry or result in disability. PGT-SR identifies the chromosomally balanced embryos for transfer.

The biopsy itself

Performed on day 5 or 6 blastocysts. A small number of trophectoderm cells (the cells that will become placenta) are sampled and sent for analysis. Embryos are vitrified (frozen) and transferred in a later cycle. Survival rates after biopsy and thaw exceed 95 percent in good labs.

Questions worth asking your doctor

• Which version of PGT, if any, are you recommending, and what specifically would it tell us?
• Given my age and our diagnosis, what does the data show about live-birth improvement with PGT-A?
• What is your clinic’s mosaic rate, and how do you handle mosaic embryos?
• What is the per-cycle and per-embryo cost, and what is the price of NOT testing?

This essay is educational. Every patient’s situation is different – the right plan is shaped in conversation with a fertility specialist who knows the full picture.