A recent study published in Aging-US reveals that smaller, hatching embryos may be more likely to be genetically healthy, providing a potential new approach for selecting embryos during in vitro fertilization (IVF), particularly in settings where advanced genetic testing is unavailable.
The research, led by Jakub Wyroba from the Malopolski Institute of Fertility Diagnostics and Treatment and Pawel Kordowitzki from Harvard Medical School, explored how the physical characteristics of embryos could predict their genetic health. This study, which included 1,150 embryos from women aged 26 to 45, focused on two key features: embryo size and whether the embryo had started hatching.
As women increasingly choose to have children later in life, the risk of chromosomal issues in embryos, such as aneuploidy, rises. Preimplantation genetic testing for aneuploidy (PGT-A) is often used to identify healthy embryos, but it is expensive and not available in all regions. The study found that, when PGT-A is not an option, the size and hatching status of embryos may offer an alternative method for predicting genetic health.
Embryos are typically cultured in the lab for several days before being transferred to the uterus, with the blastocyst stage (days five or six) marking the point at which embryos begin hatching from their outer shell, the zona pellucida. This step is crucial for implantation and pregnancy initiation.
The researchers found that smaller embryos that had already begun the hatching process were more likely to be chromosomally normal (euploid). In the study, 49% of embryos were found to be aneuploid, with a notable difference in outcomes based on size and hatching behavior. For women over 35, 51% of small, hatching embryos were euploid compared to just 38% of larger, unhatched embryos. Among younger women (under 35), 73% of small, hatching embryos were euploid, compared to 58% of large, unhatched ones.
Interestingly, when embryos were confirmed to be euploid, both large and small embryos showed similar pregnancy rates following transfer, suggesting that size and hatching status primarily matter in the absence of genetic testing.
This study provides new guidance for IVF clinics, particularly those unable to perform PGT-A, by suggesting that selecting smaller, hatching embryos could improve IVF success rates. This approach could make fertility treatments more accessible and affordable, offering hope to women, particularly those of advanced maternal age, who face greater challenges in conceiving.
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