Andersen, AG, TK Jensen, E Carlsen, N Jørgensen, AM Andersson, T Krarup, N Keiding and NE Skakkebæk. 2000. High frequency of sub-optimal semen quality in an unselected population of young men. Human Reproduction 15(2): 366-372.

Andersen et al. examined young men from the general Danish population that participated in compulsory medical examination related to military service in two Danish cities (Copenhagen and Aalborg) in two periods during 1996 and 1998. 708 participants contributed semen samples. Concerns about possible selection bias in the first period led to a less demanding protocol in the second. Subsequent analysis indicates the initial concern was not warranted.

"Surprisingly low sperm concentrations were found in this population of 18-20 year old men: the median sperm concentration of 41 million/ml was significantly lower than the values found in previous national and international studies."

The graph to the right is a frequency histogram illustrating the percentage of men contributing samples with sperm concentrations within a particular range of values.


from Andersen et al. 2000.

"It is difficult to explain the low values of sperm count in young Danish men. A short period of abstinence may contribute to a low sperm count, but even when excluding those with a period of abstinence below 48 h, more than 40% of the men had a sperm concentration below 40 million/ml."

"A significant correlation was also found between reproductive hormones, sperm count and testicular volume, indicating that low sperm counts were due to intrinsic biological factors rather than a short period of abstinence."

Andersen et al. note that Denmark has been shown to have high rates of male reproductive abnormalities, including cryptorchidism and testicular cancer

 

The sperm count is low enough to raise concerns about fertility. According to WHO guidelines, a sperm concentration below 20 million/ml is abnormal.

Andersen et al. note that this guideline is arbitrary, and point to a study (right) relating semen quality to fecundity suggesting impairments in fecundity can be observed beginning at 40 million sperm per ml.

adapted from Bonde et al. 1998
This graph plots the likelihood of pregnancy within a given menstrual cycle as a function of sperm concentration of the husband. The dotted lines are 95% confidence intervals.