A first prospective study of the individual straight line velocity of the spermatozoon and its influences on the fertilization rate after intracytoplasmic sperm injection.

The straight line velocity of 500 individual spermatozoa was measured immediately before their direct injection into the cytoplasm of 500 metaphase II oocytes. The straight line velocity (VSL) did not have a normal distribution (P < 0.01) and ranged between 0 and 35 microm/s. The fertilization rate (84%) was significantly (P < 0.008) higher in the quartile of the sperm population with the highest VSL compared to the fertilization rate (68%) in the quartile with the lowest VSL. Embryo cleavage and embryo quality were not different in the quartiles of the sperm population used for injection.