GEOGRAPHIC VARIATIONS IN SPERM COUNTS - A POTENTIAL CAUSE OF BIAS IN STUDIES OF SEMEN QUALITY

Objective: To determine whether geographic variations in sperm counts might bias conclusions drawn from studies of semen quality. Design: Re analysis of published data from a meta-analysis of 61 studies from 193 8 to 1990 that concluded a worldwide decline in semen quality over the last 50 years. Main Outcome Measures: Influence of geographic locatio n on sperm counts. Results: Of 61 studies in the meta-analysis, only 2 0 included greater than or equal to 100 men. These 20 studies collecti vely comprised 91% of the total men studied. We focused our reanalysis on these 20 studies. Of the studies before 1970, all were from the Un ited States and 80% were from New York. These studies represented loca tions with the highest sperm counts, In contrast, after 1970, 80% of t he studies were from locations not represented earlier, including five studies from third world countries, where sperm counts were low. Conc lusions: Sperm counts vary dramatically among different geographic loc ations. Geographic variations in sperm counts need to be considered wh en analyzing data from different locations.