[Role of sperm passage through cervical mucus: fertilizing capacity tested by in vitro fertilization with zona-free hamster eggs].

The effect of sperm passage through cervical mucus (CM) on the fertilizing capacity of human spermatozoa was examined in the in vitro fertilization system of zona-free hamster eggs. Each drop of ejaculated semen and BWW culture medium was connected by a small capillary tube filled with preovulatory CM, egg white or BWW medium under liquid paraffin oil in a plastic petri dish. After 2 hours, zona-free hamster eggs were added to the drop of BWW culture medium containing spermatozoa which had passed through the capillary tube and the mixture was incubated for various lengths of time at 37 degrees C under 5% CO2 in air. Human spermatozoa, which were washed and preincubated for 2 hours in BWW medium, were capable of fertilizing zona-free hamster eggs but needed a longer incubation time than spermatozoa which had passed through CM. Fertilization rates of spermatozoa which had passed through CM and egg white were very similar, but no fertilization occurred in the drop containing spermatozoa which had passed through BWW medium, presumably because of the contamination with seminal plasma. These results indicate that the most important role of CM may be to separate motile spermatozoa from seminal plasma components hostile to fertilization.