Cryopreservation of human spermatozoa. II. Postthaw chronology of motility and of zona-free hamster ova penetration.

Postthaw dynamics of motility maintenance and ability to penetrate zona-free hamster ova were examined with human sperm. Ten semen samples were each divided into two equal volumes; one was cryopreserved while the other half remained untreated. Frozen samples were thawed, and initial evaluations for motility and hamster egg penetration were made on both untreated and frozen-thawed samples. The time difference between the initial evaluations for the two treatment groups was approximately 30 minutes as a result of the time required to freeze and thaw aliquots. Subsequent evaluations were made 6, 12, 24, and 48 hours later. Over all times both the motility and fertilizability of cryopreserved spermatozoa were significantly reduced (P less than 0.05) when compared with those of untreated sperm. The pattern of motility loss over time was similar between untreated and frozen-thawed sperm (P greater than 0.10). Conversely, differences between untreated and frozen-thawed sperm in fertilizability patterns were dramatic (P less than 0.05). This was evidenced by penetration rates for cryopreserved sperm highest at 0 hour and decreasing over time, whereas penetration by untreated spermatozoa was lowest at 0 hour, increasing to a maximum at 24 hours. These observations may be important in the development of laboratory protocols for freezing and clinical protocols for using frozen-thawed sperm.