A new study led by researchers at the University of Cambridge has raised questions about the reliability of one of the most commonly used techniques for assessing embryos in IVF. Published in Nature Biotechnology, the findings indicate that preimplantation genetic testing for aneuploidy (PGT-A), which aims to identify embryos with abnormal numbers of chromosomes, may not always provide an accurate picture of an embryo’s genetic health.

PGT-A has long been used to select embryos most likely to result in successful pregnancies and healthy births. The method typically involves removing a few cells from the outer layer of the blastocyst and analysing them for chromosomal abnormalities. However, the Cambridge team’s work suggests that this sampling approach can miss abnormalities in the inner cell mass, which forms the fetus, or can overstate risks when the outer layer carries errors that would otherwise be corrected during development.

Using advanced real-time imaging and single-cell sequencing, the researchers tracked chromosomal changes in early embryos. They found that embryos frequently exhibit a degree of mosaicism, meaning that some cells carry abnormal chromosome numbers while others are normal. This dynamic process often resolves itself naturally, with healthy cells outcompeting abnormal ones as development progresses. As a result, embryos labelled as “abnormal” under current testing standards may, in fact, be viable and capable of producing healthy pregnancies.

The study also points to inconsistencies in how laboratories interpret test results. Variability in cell sampling and thresholds for determining abnormality may lead to embryos being discarded unnecessarily. These findings call for a reevaluation of how genetic screening is integrated into IVF decision-making and highlight the potential need for improved, less invasive diagnostic tools that consider the embryo as a whole rather than a static snapshot.

Clinics and embryologists may need to weigh these results carefully when counselling patients. While PGT-A can still play a valuable role in identifying major chromosomal imbalances, its limitations underscore the importance of combining genetic testing with other forms of embryo assessment, such as morphology and time-lapse imaging. Ongoing advances in multi-omic and live imaging technologies could pave the way toward more accurate, holistic embryo evaluation in the near future.

Sources

23 October 2025, University of Cambridge

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Real-time embryo imaging raises questions about IVF screening accuracy

23 October 2025, New Scientist

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