PGT, or preimplantation genetic testing, is a group of lab techniques used during IVF to check embryos for genetic or chromosomal problems before they’re transferred to the uterus. The goal is to select embryos most likely to lead to a healthy pregnancy. There are three types, each designed to catch a different category of genetic issue, and understanding the differences helps you know which one applies to your situation.
The Three Types of PGT
PGT-A (aneuploidy) checks whether an embryo has the correct number of chromosomes. Healthy human cells have 23 pairs. An embryo with too many or too few chromosomes is called aneuploid, and most aneuploid embryos either fail to implant, miscarry, or result in conditions like Down syndrome. PGT-A is the most commonly offered form and is aimed at improving pregnancy rates and reducing miscarriage risk.
PGT-M (monogenic disorders) looks for a specific gene mutation that one or both parents are known to carry. This is the type used when there’s a family history of single-gene conditions like cystic fibrosis, sickle cell disease, Duchenne muscular dystrophy, or spinal muscular atrophy. The test identifies which embryos inherited the problematic variant and which did not, so only unaffected embryos (or healthy carriers, in the case of recessive conditions) are selected for transfer.
PGT-SR (structural rearrangements) screens for problems with the physical structure of chromosomes, such as pieces that are missing, duplicated, flipped, or swapped between chromosomes. Parents who carry a balanced translocation often have no symptoms themselves but face higher rates of miscarriage or chromosomally abnormal pregnancies. PGT-SR identifies embryos that are chromosomally normal or carry a balanced rearrangement unlikely to cause problems.
How the Biopsy Works
All three types of PGT require the same physical step: a tiny biopsy taken from the embryo. After egg retrieval and fertilization, embryos are grown in the lab for about five to six days until they reach the blastocyst stage, a hollow ball of roughly 100 to 200 cells. At this point, the embryo has two distinct cell populations. The inner cell mass eventually becomes the fetus, while the outer layer, called the trophectoderm, becomes the placenta.
The biopsy targets the trophectoderm. An embryologist uses a precision laser to open the outer shell of the embryo, then gently removes five to eight cells. This avoids disturbing the inner cell mass entirely. The sampled cells are sent to a genetics lab for analysis, while the embryos are frozen and stored.
Results Timeline and Next Steps
PGT results typically come back within one to two weeks. More complex cases, particularly those involving rare chromosomal disorders, can take an additional two to four weeks. Once results are in, your clinic will walk you through which embryos are viable for transfer. Embryos that test normal are thawed and transferred in a subsequent frozen embryo transfer cycle, timed to when the uterine lining is ready.
Because all embryos must be frozen while awaiting results, PGT always means a fresh transfer on the same cycle as egg retrieval isn’t an option. This adds at least one additional cycle to the overall timeline.
How Accurate Is PGT?
Accuracy depends partly on what you’re measuring. In controlled lab settings, PGT-A achieves about 98.9% overall accuracy. But embryos aren’t uniform. A biopsy samples only a small cluster of outer cells, and those cells don’t always perfectly represent the rest of the embryo. When researchers compared biopsy results to the actual chromosomal makeup of the whole embryo, accuracy dropped to around 84%.
In clinical practice, the misdiagnosis rate after transferring an embryo labeled normal is less than 1%, according to a systematic review in Fertility and Sterility. Among pregnancy losses that occurred after transferring a supposedly normal embryo, though, about 13% turned out to involve a chromosomal mismatch, suggesting the biopsy had missed the problem. This is why many clinics still recommend standard prenatal screening (like cell-free DNA testing or amniocentesis) even after PGT.
Mosaic Embryos: A Gray Area
One of the most confusing results you can receive is “mosaic.” A mosaic embryo contains a mix of chromosomally normal and abnormal cells. This doesn’t necessarily mean the embryo is unhealthy. It may actually be fully normal, fully abnormal, or genuinely a mixture. The biopsy can only sample a handful of cells, so it’s capturing a snapshot rather than the full picture.
Mosaic embryos can and do result in healthy pregnancies. A review of 25 studies covering 2,759 mosaic embryo transfers found that fewer than 1% resulted in an ongoing pregnancy affected by the specific abnormality flagged on PGT. However, mosaic embryos do implant at lower rates and lead to more than twice the miscarriage rate compared to embryos that tested fully normal. Most clinics will discuss mosaic embryos as a secondary option if no clearly normal embryos are available.
Who Benefits Most From PGT
PGT-M and PGT-SR have clear, targeted uses: if you or your partner carry a known genetic mutation or chromosomal rearrangement, these tests directly reduce the chance of passing it on. There’s little debate about their value for the right patients.
PGT-A is more nuanced. The American Society for Reproductive Medicine’s 2024 committee opinion states that PGT-A has not been shown to benefit all IVF patients as a routine screening tool. Specifically, ASRM found insufficient evidence to recommend it for recurrent pregnancy loss, donor egg cycles, advanced paternal age, or male factor infertility. Where PGT-A does appear to help most is in patients of advanced maternal age who still have good ovarian reserve, since the rate of aneuploid embryos rises significantly with age.
A single-center retrospective study found a live birth rate of 48.3% per transfer in the PGT-A group compared to 34.7% in the conventional IVF group. Miscarriage rates were also lower: 25% with PGT-A versus 42.6% without. These numbers look encouraging, but they reflect per-transfer rates. Because PGT sometimes reduces the number of embryos available for transfer (by identifying some as abnormal), the cumulative success rate per egg retrieval cycle may narrow the gap.
What PGT Costs
PGT adds a significant expense on top of standard IVF. Published cost analyses place the combined biopsy and testing fee at roughly $3,000 to $5,000 per cycle, though some clinics charge considerably more, with estimates ranging up to $12,000 or higher depending on the number of embryos tested and the complexity of the analysis. PGT-M often costs more than PGT-A because it requires a custom test design (called a “probe”) specific to your family’s mutation, which can add $2,000 to $5,000 in upfront development before testing even begins.
Most insurance plans do not cover PGT, even when they cover IVF itself. Some clinics offer per-embryo pricing while others charge a flat rate for the cycle, so it’s worth asking how the fee structure works before committing.
Limitations Worth Understanding
PGT is a screening tool, not a guarantee. A normal result significantly improves the odds of a healthy pregnancy, but it doesn’t eliminate all genetic risk. The test only examines the specific conditions it’s designed to detect. PGT-A won’t catch single-gene disorders, and PGT-M won’t catch chromosome count errors unless PGT-A is also performed.
The biopsy itself is generally considered safe, but it is an invasive procedure on a microscopic embryo. Some embryos, particularly those that are slow to develop or poor quality, may not survive the biopsy or freeze-thaw process. And because PGT requires all embryos to reach the blastocyst stage before biopsy, patients who produce few embryos or whose embryos tend to arrest before day five may end up with nothing to test.
For patients with limited embryos, the decision becomes a tradeoff: the information PGT provides versus the small but real possibility that the biopsy or extended culture reduces the number of embryos available for transfer. This is a conversation worth having with your reproductive endocrinologist based on your specific cycle numbers and history.