News | Does IVF Embryo Screening Have a Timing Blind Spot? Genetic Changes Continue After Testing
During in vitro fertilization (IVF), embryos are often screened for chromosomal abnormalities before transfer to help select those more likely to result in pregnancy. New research suggests that a widely used test may miss some genetic abnormalities that arise between testing and implantation, although the clinical significance remains unclear.
The study by Ahmed Abdelbaki’s team at the University of Cambridge was published in Nature Biotechnology. It examined preimplantation genetic testing for aneuploidy (PGT-A), usually performed 5–6 days after fertilization by removing a few cells from the embryo’s outer layer, the trophectoderm, and checking chromosome numbers to assess miscarriage risk.
The researchers noted that PGT-A is only a snapshot of embryonic development. Cells continue dividing after testing and before transfer and implantation, and new chromosomal errors may arise during this period.
To model this window, the team continuously imaged thawed embryos for 46 hours, corresponding to the 1–5 days typically needed for implantation after transfer. Previous observations rarely exceeded 24 hours because embryos are highly light-sensitive. Light-sheet microscopy illuminated only thin sections, greatly reducing phototoxicity and enabling prolonged high-resolution observation.
Researchers injected 13 human embryos with a fluorescent DNA-binding dye and tracked chromosomes during cell division. Among 223 divisions, about 8% showed chromosome-alignment errors before division. Such errors increase the risk of missing or duplicated chromosomes in daughter cells and are associated with implantation failure, miscarriage, and conditions such as Down syndrome.
“This suggests that new genetic changes may still occur in embryos after PGT-A screening,” said Lilli Zimmerman, a reproductive medicine specialist at Northwell Health in New York.
These new errors were mainly confined to outer cells that later form the placenta, rather than the inner cell mass that develops into the fetus. Previous studies show that embryos with some abnormalities in outer cells may still implant and produce healthy pregnancies, so the effect on developmental potential remains uncertain.
Abdelbaki said the findings do not mean PGT-A has “failed,” but show that embryonic development is highly dynamic and genetic status can change. “Some later changes may not affect embryo viability.”
Zimmerman added that many questions remain about defining an embryo as genetically “normal” or “abnormal.” The study included only 13 embryos, so larger studies are needed.
Overall, the study shows that embryos may undergo genetic changes before transfer even after PGT-A. The findings may prompt further refinement of screening strategies, testing times, and interpretation.
News | Does IVF Embryo Screening Have a Timing Blind Spot? Genetic Changes Continue After Testing
News | Does IVF Embryo Screening Have a Timing Blind Spot? Genetic Changes Continue After Testing
During in vitro fertilization (IVF), embryos are often screened for chromosomal abnormalities before transfer to help select those more likely to result in pregnancy. New research suggests that a widely used test may miss some genetic abnormalities that arise between testing and implantation, although the clinical significance remains unclear.
The study by Ahmed Abdelbaki’s team at the University of Cambridge was published in Nature Biotechnology. It examined preimplantation genetic testing for aneuploidy (PGT-A), usually performed 5–6 days after fertilization by removing a few cells from the embryo’s outer layer, the trophectoderm, and checking chromosome numbers to assess miscarriage risk.
The researchers noted that PGT-A is only a snapshot of embryonic development. Cells continue dividing after testing and before transfer and implantation, and new chromosomal errors may arise during this period.
To model this window, the team continuously imaged thawed embryos for 46 hours, corresponding to the 1–5 days typically needed for implantation after transfer. Previous observations rarely exceeded 24 hours because embryos are highly light-sensitive. Light-sheet microscopy illuminated only thin sections, greatly reducing phototoxicity and enabling prolonged high-resolution observation.
Researchers injected 13 human embryos with a fluorescent DNA-binding dye and tracked chromosomes during cell division. Among 223 divisions, about 8% showed chromosome-alignment errors before division. Such errors increase the risk of missing or duplicated chromosomes in daughter cells and are associated with implantation failure, miscarriage, and conditions such as Down syndrome.
“This suggests that new genetic changes may still occur in embryos after PGT-A screening,” said Lilli Zimmerman, a reproductive medicine specialist at Northwell Health in New York.
These new errors were mainly confined to outer cells that later form the placenta, rather than the inner cell mass that develops into the fetus. Previous studies show that embryos with some abnormalities in outer cells may still implant and produce healthy pregnancies, so the effect on developmental potential remains uncertain.
Abdelbaki said the findings do not mean PGT-A has “failed,” but show that embryonic development is highly dynamic and genetic status can change. “Some later changes may not affect embryo viability.”
Zimmerman added that many questions remain about defining an embryo as genetically “normal” or “abnormal.” The study included only 13 embryos, so larger studies are needed.
Overall, the study shows that embryos may undergo genetic changes before transfer even after PGT-A. The findings may prompt further refinement of screening strategies, testing times, and interpretation.
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