Technique to examine human sperm chromosomes using zona-free hamster eggs

In experiments with repeated semen samples from two donors, zona-free hamster eggs were used for activation of human spermatozoa to metaphase. When mean number of spermatozoa per penetrated egg was low (1.0-3.3) after insemination in vitro, further incubation resulted in activation of spermatozoa to metaphase. High sperm/egg ratios, 4.2 and 7.5, yielded no sperm chromosomes. The preincubation and insemination intervals necessary for low sperm/egg ratios were individual.