News | Are Smaller Hatching Embryos More Likely to Have Healthy Chromosomes? A New Approach to IVF Embryo Selection
Accurately assessing an embryo’s chromosomal health is a key factor in IVF success. A recent study by the Malopolski Institute of Fertility Diagnostics and Treatment, Harvard Medical School, Nicolaus Copernicus University, and Charité in Berlin found that smaller embryos that have begun hatching are more likely to be chromosomally normal, or euploid.
The study, titled Reproductive aging, preimplantation genetic testing for aneuploidy, and the diameter of blastocysts: does size matter?, was published in volume 17, issue 3 of Aging in 2025. Analysis of embryos from 1,150 IVF cycles showed that embryo size and whether hatching from the zona pellucida had begun may be useful indicators of chromosomal health.
Later Childbearing Drives Advances in Embryo Selection
As more women try to conceive after age 30 or even 40, reproductive aging has become a major challenge in assisted reproduction. Oocytes from older women are more likely to have chromosomal aneuploidy, which substantially reduces implantation and pregnancy rates and increases miscarriage risk.
Preimplantation Genetic Testing for Aneuploidy (PGT-A), widely used in fertility clinics, can detect chromosomal abnormalities in embryos. However, PGT-A is costly, technically demanding, and unavailable in many countries. The new study explored whether embryo morphology could provide a useful assessment when PGT-A is unavailable.
Smaller Embryos That Have Begun Hatching Are More Likely to Be Euploid
The embryos came from women aged 26 to 45. Researchers examined two main features:
1.Embryo diameter at the blastocyst stage, usually day 5 or 6 of culture
2.Whether the embryo had begun hatching from the zona pellucida
Overall, about 49% of embryos were chromosomally abnormal, or aneuploid. Smaller blastocysts that were hatching, however, were significantly more likely to be chromosomally normal, or euploid.
Among women over 35, 51% of small hatching embryos were euploid, compared with 38% of large non-hatching blastocysts;
Among women under 35, the difference was greater: 73% of small hatching embryos were euploid, compared with 58% of large non-hatching blastocysts.
Is Bigger Not Always Better? Rethinking Embryo Selection
Although larger embryos may appear more mature, the study indicates that size does not equal quality. Where PGT-A is unavailable, clinicians could combine hatching status and embryo diameter as a cost-effective alternative assessment.
When an embryo was already known to be euploid after PGT-A, pregnancy rates after transfer were similar regardless of size. This further suggests that size and hatching status are most useful for embryo selection when genetic testing is unavailable.
Clinical Potential: Lower-Cost, More Precise Embryo Selection
Corresponding author Dr. Pawel Kordowitzki of Harvard Medical School and Charité in Berlin said the study provides a new, measurable embryo-selection tool, particularly for regions without access to PGT-A. By assessing blastocyst hatching and size, clinicians may be able to improve embryo transfer success at lower cost.
As assisted reproduction becomes more widely used, this combination of morphology and hatching behavior may support broader clinical embryo selection and offer a practical option for more families.
News | Are Smaller Hatching Embryos More Likely to Have Healthy Chromosomes? A New Approach to IVF Embryo Selection
News | Are Smaller Hatching Embryos More Likely to Have Healthy Chromosomes? A New Approach to IVF Embryo Selection
Accurately assessing an embryo’s chromosomal health is a key factor in IVF success. A recent study by the Malopolski Institute of Fertility Diagnostics and Treatment, Harvard Medical School, Nicolaus Copernicus University, and Charité in Berlin found that smaller embryos that have begun hatching are more likely to be chromosomally normal, or euploid.
The study, titled Reproductive aging, preimplantation genetic testing for aneuploidy, and the diameter of blastocysts: does size matter?, was published in volume 17, issue 3 of Aging in 2025. Analysis of embryos from 1,150 IVF cycles showed that embryo size and whether hatching from the zona pellucida had begun may be useful indicators of chromosomal health.
Later Childbearing Drives Advances in Embryo Selection
As more women try to conceive after age 30 or even 40, reproductive aging has become a major challenge in assisted reproduction. Oocytes from older women are more likely to have chromosomal aneuploidy, which substantially reduces implantation and pregnancy rates and increases miscarriage risk.
Preimplantation Genetic Testing for Aneuploidy (PGT-A), widely used in fertility clinics, can detect chromosomal abnormalities in embryos. However, PGT-A is costly, technically demanding, and unavailable in many countries. The new study explored whether embryo morphology could provide a useful assessment when PGT-A is unavailable.
Smaller Embryos That Have Begun Hatching Are More Likely to Be Euploid
The embryos came from women aged 26 to 45. Researchers examined two main features:
1.Embryo diameter at the blastocyst stage, usually day 5 or 6 of culture
2.Whether the embryo had begun hatching from the zona pellucida
Overall, about 49% of embryos were chromosomally abnormal, or aneuploid. Smaller blastocysts that were hatching, however, were significantly more likely to be chromosomally normal, or euploid.
Among women over 35, 51% of small hatching embryos were euploid, compared with 38% of large non-hatching blastocysts;
Among women under 35, the difference was greater: 73% of small hatching embryos were euploid, compared with 58% of large non-hatching blastocysts.
Is Bigger Not Always Better? Rethinking Embryo Selection
Although larger embryos may appear more mature, the study indicates that size does not equal quality. Where PGT-A is unavailable, clinicians could combine hatching status and embryo diameter as a cost-effective alternative assessment.
When an embryo was already known to be euploid after PGT-A, pregnancy rates after transfer were similar regardless of size. This further suggests that size and hatching status are most useful for embryo selection when genetic testing is unavailable.
Clinical Potential: Lower-Cost, More Precise Embryo Selection
Corresponding author Dr. Pawel Kordowitzki of Harvard Medical School and Charité in Berlin said the study provides a new, measurable embryo-selection tool, particularly for regions without access to PGT-A. By assessing blastocyst hatching and size, clinicians may be able to improve embryo transfer success at lower cost.
As assisted reproduction becomes more widely used, this combination of morphology and hatching behavior may support broader clinical embryo selection and offer a practical option for more families.
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