Biochemical factors affecting the fertility of cryopreserved human semen.

The effects of dilution and cryopreservation on biochemical, fine structural and conventional semen parameters were studied and correlated with an index of fertility. Dilution of semen had major effects on the parameters studied. Freezing and thawing further reduced motility and the proportion of viable spermatozoa, and increased the proportion of spermatozoa with damaged membranes. The fertility index of donors was positively correlated with sperm concentration, seminal plasma protein concentration, damage to sperm head membranes and the proportion of spermatozoa with intact acrosomes prior to dilution or after freezing and thawing. Seminal plasma [Na+], [Ca2+], Ca2+/Mg2+-ratios and the change in [K+] were negatively correlated with fertility index. Multiple regression analysis revealed that [Na+] in seminal plasma, and sperm concentration in semen prior to dilution and freezing, contribute to 68% of the variation in fertility of cryopreserved semen.