PGT-A screens a small biopsy from an embryo for the wrong number of chromosomes. It can help identify embryos less likely to implant or more likely to miscarry, but it cannot guarantee a pregnancy, it cannot see everything, and its value as a routine test for all IVF patients has not been established. Whether it makes sense for you is a decision to make with your clinician and, ideally, a genetic counselor.
Preimplantation genetic testing for aneuploidy, or PGT-A, is one of the most debated parts of modern IVF. It is widely offered, it is often priced as an add-on, and the way it is described can make it sound more definitive than the science allows. This guide explains what it does, what it cannot do, and what to ask. It is not about selecting for traits, and it is different from the AI embryo selection tools and the carrier screening that couples do before pregnancy.
What PGT-A Is Checking
Most human embryos that fail to implant, or that miscarry, have an abnormal number of chromosomes, a condition called aneuploidy. The risk rises with the age of the egg. In PGT-A, an embryologist removes a few cells from the outer layer of a day 5 to 7 embryo (the part that becomes the placenta), the embryo is frozen, and the cells are sent to a lab that counts chromosomes. A result of "euploid" means the sample showed the usual number of chromosomes, and "aneuploid" means it did not.
PGT-A is a screening test. It is not the same as PGT-M, which tests for a specific inherited single-gene condition a family is known to carry, or PGT-SR, which looks for structural chromosome rearrangements. Those are chosen for specific, known reasons.
What the Major Medical Bodies Say
The American Society for Reproductive Medicine's 2024 committee opinion on PGT-A reviewed the evidence and reached a cautious conclusion. It stated that the value of PGT-A as a screening test for all IVF patients has not been established, and that two recent multicenter randomized trials found overall pregnancy outcomes were similar to conventional IVF. The authors concluded that routine blastocyst biopsy with aneuploidy testing for all infertile IVF patients cannot be recommended. They also emphasized that the best approach depends on the individual patient, and that not testing is a legitimate alternative patients should be told about.
In the UK, the fertility regulator HFEA rates PGT-A red for chance of a baby on its traffic-light add-on scheme, a rating that flags possible safety concerns or evidence that an add-on may reduce effectiveness, and NICE's fertility guidance recommends against offering it to improve live birth rates. These are UK positions, and US practice differs, but they show how divided expert opinion is.
PGT-A may change which embryo is transferred first and sometimes how many transfers are needed. It does not create healthier embryos, and it does not increase the number of embryos you have. Some people find that reassuring, others find it adds stress.
Where It May Help, Where the Evidence Is Weaker
- Where clinics more often offer it: advanced maternal age, repeated implantation failure or pregnancy loss, where the chance that any given embryo is aneuploid is higher. The ASRM opinion notes that cost-effectiveness is hard to quantify, improves with age and with the number of blastocysts available, and was not favorable in some settings, such as unexplained recurrent pregnancy loss. See our guide to recurrent pregnancy loss evaluation for related testing.
- Evidence is weaker: as a default test for everyone, particularly for younger patients with several embryos.
- Not a fit for everyone: if you only have one or two embryos, testing may leave you with fewer options without improving your odds.
The Limits Nobody Mentions Enough
It tests a sample, not the whole embryo
The biopsy covers a handful of cells from the outer layer. ASRM notes it is unclear how well that sample represents the whole embryo. A result may not match what is happening in the part that becomes the baby.
False positives can discard embryos that might have worked
An aneuploid result can occasionally be wrong. The ASRM opinion discusses that a false-positive result may lead to embryos being discarded that could have produced healthy births. It also notes the data on how often this happens is limited, so ask your clinic how they handle borderline results.
Mosaic results are the gray zone
Sometimes a sample has a mix of normal and abnormal cells, called mosaic. ASRM's separate committee opinion on mosaic results explains that a mosaic call is inferred from intermediate copy numbers, and that technical noise, amplification bias and contamination can produce similar results. Labs also report mosaicism at very different rates, so the same biopsy could be labeled differently by two labs. Some mosaic embryos have led to healthy babies, but there is no validated way to rank them. The opinion strongly recommends genetic counseling before transferring a mosaic embryo, and notes that routine noninvasive prenatal testing is not designed to detect mosaicism, so diagnostic testing such as CVS or amniocentesis is needed to confirm a concern.
No result is possible
A biopsy can come back with no usable result. Informed consent should cover this, along with mosaic or segmental findings and the chance of misdiagnosis.
Questions to Ask Before You Agree
Bring This List
These questions fit alongside the broader guide to IVF add-ons and the questions to ask before paying extra. If you want to think through what happens to any embryos that are not transferred, read what happens to unused embryos.
Testing Does Not Mean a Guarantee
Even a euploid embryo does not always result in a pregnancy, and a pregnancy can still miscarry for other reasons. PGT-A does not screen for most single-gene conditions, birth defects or health problems that develop later. Take a break from internet forums that treat "a normal embryo" as a promise. It is a better-than-average starting point, not a certainty. If you want to understand the odds and how clinics report them, our IVF myths debunked post is a useful companion.
Frequently Asked Questions
The Bottom Line
PGT-A can be a useful tool for some patients and an expensive extra for others. The honest summary is that it can help rank embryos, it cannot guarantee a pregnancy, and large trials have not shown it improves outcomes for every IVF patient. Ask why your clinic recommends it for you, find out how mosaic and abnormal results are handled before you test, and consider a genetic counseling visit. Then choose what fits your age, your embryo count and your values.