Time-lapse analysis of cleavage stage mouse embryos reveals that developmental kinetics are related to subsequent blastocyst metabolism (#140)
Time-lapse analysis of embryo developmental kinetics allows the timing of cleavage divisions to be accurately determined. Previous work has revealed a distribution of cleavage timings in mouse embryos, with faster cleavage, especially the time of 2-cell division, associated with higher rates of blastocyst formation. However, the relationship between metabolism of embryos of different cleavage rates is not known. The aim of this study was therefore to determine how blastocyst quality, in terms of cell number and metabolism (a higher glucose uptake and a lower glycolytic rate being associated with higher viability), is related to cleavage kinetics. In vitro fertilised C57BL/6 x CBA (F1) mouse zygotes were cultured in a time-lapse incubator, with images recorded every 15 minutes. It was found that the faster the timing of 2- to 6- cell division, the higher the blastocyst cell number (p<0.0001). When embryos were sorted into quartiles with respect to 2-cell cleavage timings, it was found that the fastest embryos (first quartile) cleaved on average 2.5h earlier than the slowest embryos (fourth quartile) (10.6 ± 0.1h vs. 13.1 ± 0.1h, p<0.0001), and that this was associated with a significant difference in blastocyst total cell number on day 5 (87.0 ± 4.3 vs. 71.3 ± 3.3, p<0.005). Ultramicrofluorescence analysis of the ‘fast’ and ‘slow’ embryos showed a significant difference in glucose consumption per embryo (20.9 ± 1.2 pmol/hr vs. 13.3 ± 0.9 pmol/hr, p<0.001) and lactate production per embryo (23.4 ± 2.0 pmol/hr vs. 17.1 ± 1.3 pmol/hr, p<0.05). Glycolytic rate was significantly lower in the ‘fast’ embryos (55.5 ± 3.6% vs. 69.0 ± 6.2%, p<0.05). This study has shown for the first time that a morphokinetic marker of development during the cleavage stages is related to subsequent blastocyst metabolism. Further work is ongoing to determine if such parameters in combination can increase embryo selection efficacy.