Freezability and semen parameters in candidates of sperm bank donors: 1992-2010

There has been considerable concern worldwide about possible semen quality deterioration over the last 2 decades. The aim of this study was to evaluate freezability and semen quality of healthy young males during the years 1992-2010. A total of 1211 young (20-32 years old) candidates for sperm bank donation were recruited into the study with no exclusion criteria. They were instructed to observe 2 to 3 days of abstinence from sexual activity, and most of them supplied 2 specimens each. Average values of the various semen parameters, including freezing survival, were calculated for each participant. The change in different semen parameters over years, according to yearly and monthly average temperatures, was evaluated by SAS PROC SURVEYREG analysis. During that period, there were significant increases in motility and vitality percentages, as well as in the percentage of thawed sperm motility. The parameters of volume, concentration, normal morphology, total count, and total motile count showed a significant decrease with years (P, <.01). The significant increase in average yearly temperature (P, <.004) had limited, nonsignificant association with any of the semen variables. However, average monthly temperature contributed significantly to the trend of semen quality parameters (ie, specimen volume, concentration, percentage of normal morphology, and thawed motility). To the best of our knowledge, this is the first demonstration of the occurrence of an improvement in percent thawed motility over the years, and its significance lies in enabling a higher proportion of sperm bank candidates to be suitable for donation. It is suggested that the global warming phenomenon might have only partial contribution to semen variable changes over the years.