High rate of mixoploidy among human blastocysts cultured in vitro

Objective: To determine the incidence and type of mixoploidy in human blastocysts produced in vitro. Design: A laboratory study of spare blastocysts from an IVF program. Setting: University hospital laboratory. Patient(s): Thirty-nine couples undergoing IVF or intracytoplasmic sperm injection. Intervention(s): A total of 103 blastocysts were classified as good- or poor-quality blastocysts based on morphology. A total of 6,927 interphase nuclei, 5,015 from 59 good-quality and 1,912 from 44 poor-quality blastocysts, were assessed for ploidy by fluorescence in situ hybridization with chromosome-specific DNA probes. Main Outcome Measure(s): The percentage and the type of polyploid cells present in each blastocyst. Result(s): Mixoploidy (mixture of diploid and polyploid cells) was found in 86% of good-quality and 82% of poor-quality blastocysts analyzed. The type of polyploidy ranged from 3N to 14N, with tetraploidy being the most common between both groups. The proportion of polyploid cells per mixoploid blastocyst ranged from 1% to 88%. The percentage of polyploid nuclei within most good-quality mixoploid blastocysts was small (10%) and significantly lower than in poor-quality blastocysts (19%). Conclusion(s): Most human blastocysts produced in vitro contain polyploid, predominantly tetraploid cells. The proportion of polyploid cells in the majority of good-quality blastocysts is low. The small numbers of blastocysts with a high percentage of polyploid cells may have implications for blastocyst transfer.