Successful fertilization in humans, achieved when parental chromosomes intermix at first mitosis, requires centrosome restoration and microtubule-mediated motility. Imaging of inseminated human oocytes reveals that the sperm introduces the centrosome. The centrosome then nucleates the new microtubule assembly to form the sperm aster--a step essential for successful fertilization. Oocytes from some infertile patients failed to complete fertilization because of defects in uniting the sperm and egg nuclei, indicating that failure to properly effect the cytoplasmic motions uniting the nuclei results in human infertility. These discoveries have important implications for infertility diagnosis and managing reproduction.

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Three mouse embryo bioassays [mouse one-cell and two-cell embryos and in vitro fertilization (IVF)] were tested for their ability to discriminate between three sources of water for medium preparation: tap water, high-performance liquid chromatography (HPLC)-grade water, and Milli-Q purified water. No differences could be detected using these assays. The lack of sensitivity of the mouse bioassays could not be attributed to the protein source or medium type. The hamster sperm motility assay (HSMA) permitted quantitative discrimination between water sources (Milli-Q greater than HPLC greater than tap). Media prepared for use in human IVF using water that exceeded minimal HSMA quality standards resulted in pregnancy rates that were greater than those attained with a lot of HPLC water that did not meet these standards. The HSMA can serve as a basis for a quality-control program in the human IVF laboratory.

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