Canadian semen quality: an analysis of sperm density among eleven academic fertility centers

OBJECTIVE: To determine whether sperm quality has declined among Canadian men during the past 13 years and whether there are regional differences in sperm quality. DESIGN: Retrospective temporal series of cross-sectional studies. SETTING: University fertility centers across Canada. PATIENT(S): Men being investigated as part of the normal infertility work-up. MAIN OUTCOME MEASURE(S): Sperm concentrations among all the samples were compared on an annual basis to assess any changes over 13 years from 1984 through 1996. RESULT(S): There were regional differences and trends in both up and down directions. Linear regression analysis of the means of each center for each year showed no significant trend. However, when all the samples were analyzed by regression analysis there was a significant downward trend. CONCLUSION(S): Linear regression analysis showed a significant downward trend in sperm concentration among 48,968 samples from Canadian men obtained from 1984 through 1996. A significant difference was seen in the mean concentrations between centers, ranging from 48.6 to 104.5 X 10(6)/mL. Secular trends in sperm density are dependent on the statistical method used for analysis.