Preimplantation Genetic Testing of embryos for aneuploidy, aka PGT-A. I bet most people have never said those words together in a sentence until you entered the world of IVF.
PGT-A involves taking embryos created through IVF and removing a few cells and analyzing them for their chromosomes. The chromosomes are counted and examined. A report on the embryo is then provided labelling the embryo as likely:
- Euploid - a “normal” number and structure of chromosomes (23 pairs)
- Mosaic - a mix of cells with the normal number and abnormal number of chromosomes
- Aneuploid - an abnormal number of chromosomes
Sometimes it comes back "failed QC" meaning the biopsy was possibly too small, or they could not analyze the chromosomes properly for some reason.
The literature suggests people over age 35 (age of the person contributing the eggs to the embryo) benefit from PGT and those under 35 do not benefit. For those under 35 they will often still do PGT-A if they have a history of repeated miscarriages, repeated failed IVF embryo transfers or are using a surrogate.
There is a group of patients who do NOT do PGT-A and regret it. It is my experience that patients in their early 30s who make embryos and have an unsuccessful embryo transfer(s) will naturally ask “why did it fail?” The most likely reason an embryo transfer fails is that the embryo was aneuploid (abnormal chromosome number or structure). After a failed embryo transfer, or two, patients sometimes wish they had tested their embryos to know with more certainty whether the embryo will implant.
This is the main value of PGT-A: transferring a chromosomally normal embryo reduces the chance you will have an unsuccessful embryo transfer or a miscarriage.
Suppose you have embryos frozen that you did NOT test with PGT. Should you thaw them now and biopsy them for PGT-A? Meaning the embryo was frozen untested and it would then be thawed, biopsied for PGT, and re-frozen.
A meta-analysis published this year helps answer this question (1).
In this analysis, the authors found the process of thawing, biopsying and re-freezing harmful to the embryo - reducing the live birth rate and increasing the miscarriage rate. The live birth rate was approximately 19% lower than if the embryo had not been thawed and biopsied.
So, what should people do? If you have untested embryos and you wish you had tested them, it is best to just keep using them, untested. Consider transferring more than one to increase the chance of success per transfer, if you and your doctor think it’s acceptable to risk a twin pregnancy.
Embryos are fragile. There is potential harm to freezing and thawing embryos and putting them through it more than once is, not surprisingly, harmful. For some people that risk of harm is worth taking, but for most people they should just keep using their frozen untested embryos and hope it is normal. Normal embryos make healthy babies whether they were tested or not.
(1) Reference: Yang Y, Li D, Liu Y, Qi Y, Li H, Wang Z, Ma B. Systematic review and meta-analysis of the impact of the refreezing and rebiopsy embryos on reproductive outcomes in patients undergoing freeze-thaw embryo transfer. Fertil Steril. 2025 Jun;123(6):1051-1061.
