Increased Blastomere Number in Cleavage-stage Embryos is Associated with Higher Aneuploidy

Objective: To evaluate the relationship between blastomere number and aneuploidy.

Design: Historical cohort study.

Setting: In vitro fertilization clinic.

Patient(s): Two hundred fifty-nine patients undergoing in vitro fertilization (IVF) in combination with comprehensive chromosomal screening of embryos.

Intervention(s): A total of 1,915 embryos were biopsied on day 3 and underwent comprehensive chromosomal screening with microarray-based comparative genomic hybridization.

Main Outcome Measure(s): Relationship between day 3 blastomere number, aneuploidy rate, and progression to the blastocyst stage.

Result(s): A number of day 3 blastomeres >9 was associated with significantly increased aneuploidy rates. Rapidly developing embryos were significantly more likely to blastulate regardless of their chromosomal status. Number of embryos per patient greater than 13 was independently associated with lower aneuploidy rates after controlling for maternal age. This trend was not significant with the use of a more clinically relevant threshold of greater than six embryos per patient.

Conclusion(s): Embryos with 6-9 cells at the cleavage stage should be considered for transfer over embryos with >9 cells. Day 3 blastomere number may be used in conjunction with extended culture to improve selection of euploid embryos, especially when supernumerary embryos are available. Further studies are needed to show if these selection criteria improve clinical outcomes.