PGT-A contamination, sometimes reported as “no result,” is poorly studied, but a 2026 study found it’s rare and that undetected contamination can distort PGT results, highlighting the importance of contamination detection in testing.
PGT-A relies on analyzing DNA from a very small number of cells taken from the embryo’s trophectoderm. Because the sample is so small, even a small amount of contaminating DNA could affect the result.
Contaminating DNA could come from residual cumulus cells, which can sometimes still be attached to the blastocyst, or from people involved in the IVF and testing process, such as the embryologist performing the biopsy or the technician handling the DNA analysis during PGT-A.
Surprisingly little research has examined how often contamination actually occurs in embryo biopsies used for PGT-A, or how much it could affect embryo classification.
A new study by Clark et al. (2026) analyzed 57,292 embryo biopsy samples from 32 IVF clinics to estimate how often contamination occurs during PGT-A and how much it could potentially distort chromosomal results.
The research was performed by the PGT lab Juno Genetics and included biopsy samples submitted for PGT-A from 32 European/UK IVF clinics that used their testing service.
Juno offers PGTseq, a PGT platform that combines NGS with SNP marker analysis. NGS is used to estimate chromosome copy number, while the SNP data provides additional genetic signals. Because each embryo should have a consistent SNP pattern, DNA from another source can create unusual patterns that reveal contamination in the biopsy sample.
Before analyzing the clinical samples, the researchers validated the PGTseq method by mixing embryo DNA with different amounts of contaminating DNA. Contamination was reliably detected when it made up about 20–80% of the DNA, but lower levels (<20%) often went undetected, meaning small amounts of contaminating DNA could potentially be missed.
For more background, check out my Complete guide to PGT-A.
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Contamination was rare but varied between clinics
DNA contamination was detected in 256 out of 57,292 biopsy samples (0.45%), or about 1 in 222 samples.
However, contamination rates varied widely between clinics, ranging from 0% to 1.68%.
Clinics reporting 0% contamination all had small sample sizes (≤173 samples), meaning contamination might have been missed. Similarly, clinics with contamination rates above 1% also tended to have smaller sample sizes (≤250 samples), which could exaggerate the percentage.
Even among clinics that had a large sample size, there were wide differences. For example, one clinic had a contamination rate of 0.14% (7/5179) while another had 0.75% (23/3066), about five times higher.
There was no statistical differences between the number of biopsies a clinic performed and the likelihood of contamination, so clinics that perform fewer (or more) biopsies all had about the same chance of contamination.
Overall, this suggests that contamination is rare but it varies substantially between IVF clinics, likely due to differences in biopsy technique or laboratory practices.
Contamination could distort PGT-A results
When contamination was detected in a biopsy sample, the result was reported as “no result”, and clinics were typically advised to perform a second biopsy of the embryo (166 samples).
By comparing contaminated samples with the results from rebiopsied embryos, the researchers estimated that 44.5% would likely have received an incorrect PGT-A classification if the contamination had not been identified. In other words, contamination could have distorted results in about half of contaminated samples if it hadn’t been detected.
This distortion occurred in two ways:
- About 20.6% of contaminated samples produced false negative results, where an aneuploid embryo appeared mosaic, likely due to contaminating DNA from a euploid source (usually cumulus cells, but sometimes DNA from lab members). When this contaminating euploid DNA mixes with aneuploid DNA from an embryo, it can dilute the abnormal signal, causing the result to appear in the mosaic range.
- Another 23.9% of contaminated samples produced false positive results, where a euploid (diploid) embryo appeared triploid. This can occur when DNA from a male embryo (XY) mixes with female contaminating DNA (XX), altering the relative amounts of X and Y chromosome DNA in a pattern that resembles XXY triploid embryos. Other embryo and contamination combinations could also distort chromosome signals and produce results that appear non-diploid. In these cases, embryos that were actually normal could potentially be misclassified as abnormal and discarded.
Conclusion
This study showed that DNA contamination during embryo biopsy is rare, occurring in about 0.45% of samples (about 1 in 222). In some cases, contamination could make abnormal embryos appear mosaic or cause normal embryos to appear abnormal.
It’s important to note that this study was conducted by the PGT lab Juno Genetics, so similar analyses across other testing platforms will be important to confirm that the results are consistent.
Juno Genetics’ PGTseq isn’t the only PGT method that detects contamination. For example, Igenomix’s Smart PGT-A Plus also combines NGS with SNP analysis to help identify contamination, and other PGT labs likely also offer similar capabilities.
This study highlights the importance of contamination detection in PGT testing, since undetected contamination can distort results. Some labs may already use these kinds of platforms and report affected samples as “no result” so the embryo can be rebiopsied.
Another important consideration is that most clinics in this study had been using Juno’s platform for at least three years. During that time, Juno notified clinics when contamination was detected, giving them an opportunity to review and potentially improve their laboratory procedures. Because of this, the contamination rates reported in this study may underestimate the true incidence of contamination in clinics where it’s not actively monitored.
Want to read more about PGT-A?
This post covers PGT-A (formerly called PGS testing), including how it works, how accurate it is, whether it can damage embryos, how to read PGT-A reports, success rates, mosaic embryos, and why even euploid embryos sometimes fail. Read more.
This post traces the evolution of PGT-A testing in IVF, from early FISH and microarray methods to modern NGS and emerging technologies like nanopore sequencing, highlighting how each advancement improved accuracy, speed, and embryo assessment. Read more.
A 2024 meta-analysis combined the results of 10 studies to show that embryos that are thawed for PGT-A, or rebiopsied after inconclusive results, have lower chances of pregnancy and live birth, with higher miscarriage rates. Read more.
The ASRM has released their 2024 committee opinion on the use of PGT-A, covering the use of PGT-A for patients with a good prognosis, advanced age, donor eggs, recurrent pregnancy loss and more. Read more.
Reference
About Embryoman
Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.