Geographic variations in sperm counts: a potential cause of bias in studies of semen quality

Fertil Steril. 1996 May;65(5):1044-6. doi: 10.1016/s0015-0282(16)58284-3.


Objective: To determine whether geographic variations in sperm counts might bias conclusions drawn from studies of semen quality.

Design: Reanalysis of published data from a meta-analysis of 61 studies from 1938 to 1990 that concluded a worldwide decline in semen quality over the last 50 years.

Main outcome measures: Influence of geographic location on sperm counts.

Results: Of 61 studies in the meta-analysis, only 20 included > or = 100 men. These 20 studies collectively comprised 91% of the total men studied. We focused our reanalysis on these 20 studies. Of the studies before 1970, all were from the United States and 80% were from New York. These studies represented locations with the highest sperm counts. In contrast, after 1970, 80% of the studies were from locations not represented earlier, including five studies from third world countries, where sperm counts were low.

Conclusions: Sperm counts vary dramatically among different geographic locations.

MeSH terms

  • Bias
  • Humans
  • Infertility, Male / epidemiology
  • Male
  • Semen / physiology*
  • Sperm Count*