Trends in semen parameters in the northeast of Scotland

The data on trends in semen quality are conflicting and sensitive to geographical variations. Although previous British surveys on semen quality indicate a decline, the northeast of Scotland has never been included in these surveys. This is an area with low out migration rates where andrology services for a population of 500 000 are centralized within a single laboratory, thus providing a unique opportunity to study population-based trends in semen quality over time. We investigated trends in semen parameters between 1994-2005, in a cohort of 4832 men attending for routine semen analysis at the Aberdeen Fertility Centre who had a sperm density of greater than 20 million per mL. The main outcome measures were trends in sperm density, sperm motility and motile density in the first semen sample. Linear regression and time series analysis were used to examine trends over time in the semen parameters. The mean and standard deviation (SD) age of all men (n=5204) in the study was 34(6) years. The median (inter quartile range) for sperm density and motile density for the study population were 61 (40-91) million/mL and 99 (47-181) million. The mean (SD) sperm motility was 49 (19)%. Among 4832 men (with sperm count >20 million per mL), data adjusted for age and period of abstinence showed a decreasing trend for sperm density over time, R2=0.45 (P=.017). There was no such trend in sperm motility and motile density. However, this trend has to be interpreted with caution due to fluctuations in semen parameters, population bias and the retrospective nature of the analysis.