Reduced penetration of zona-free hamster ova by cryopreserved human spermatozoa

The effect of cryopreservation on human sperm fertilizing potential was assessed by using the human sperm penetration into zona-free hamster ovum test. Semen samples from 12 fertile men were compared before and after cryopreservation for motility, sperm penetration rate, and number of sperm cells incorporated per oocyte. In fresh samples sperm concentration was 102 +/- 51 X 10(6) cells/ml, motility 66 +/- 14%, penetration rate 77.8 +/- 19%, and sperm incorporation 4.3 +/- 3.9 sperm per ovum. Frozen-thawed sperm cells showed a marked reduction of 61 +/- 21% (p less than 0.001) in motility. Penetration rate was reduced by 53 +/- 34% (p less than 0.01), and sperm incorporation dropped by 50 +/- 28% (p less than 0.05). Despite this substantial reduction in all three parameters, 75% of the samples maintained a penetration rate exceeding 14%, which is the lower limit for fertile semen. For the individual subject the decrease in sperm motility did not reflect actual fertility potential as expressed by its ability to penetrate zona-free hamster ova. These findings are related to morphological and biochemical changes in frozen-thawed semen and apparently are correlated with the decrease in pregnancy rates after cryopreservation. This test may be a valuable supplement to routine microscopic semen analysis for semen cryopreservation candidates.