Dynamic blastomere behaviour reflects human embryo ploidy by the four-cell stage

Area of Science:

• Reproductive Biology
• Developmental Biology
• Genetics

Background:

• Aneuploidy, an abnormal chromosome number, is frequent in human embryos (50-80%) at the cleavage stage.
• The relationship between early blastomere behavior and embryonic ploidy remains incompletely understood.

Purpose of the Study:

• To investigate if blastomere behavior during the first two cleavage divisions can predict ploidy in human embryos.
• To correlate cell cycle parameters and fragmentation with euploidy and aneuploidy.

Main Methods:

• Combined non-invasive time-lapse imaging with karyotypic reconstruction of all blastomeres.
• Analyzed four-cell stage human embryos to assess cell cycle parameter timing and fragmentation.
• Correlated observed parameters with the ploidy status of each embryo.

Main Results:

• Euploid embryos consistently exhibited precise cell cycle parameter timing.
• Only 30% of aneuploid embryos showed cell cycle parameter values within normal timing windows.
• Human embryonic aneuploidy arises from complex processes, including chromosome fragments and micronuclei, which can persist or be reabsorbed.

Conclusions:

• Cell cycle and fragmentation parameters of individual blastomeres are diagnostic of ploidy.
• These parameters are suitable for automated tracking algorithms.
• Findings suggest clinical relevance for selecting embryos with reduced miscarriage risk.