Threshold values for sperm concentration, motility, and morphology can be used to classify men as subfertile, of indeterminate fertility, or fertile. None of the measures, however, are diagnostic of infertility.

Although geographic variation in semen quality has been reported, this is the first study in the United States to compare semen quality among study centers using standardized methods and strict quality control. We evaluated semen specimens from partners of 512 pregnant women recruited through prenatal clinics in four U.S. cities during 1999-2001; 91% of men provided two specimens. Sperm concentration, semen volume, and motility were determined at the centers, and morphology was assessed at a central laboratory. Study protocols were identical across centers, and quality control was rigorously maintained. Sperm concentration was significantly lower in Columbia, Missouri, than in New York, New York; Minneapolis, Minnesota; and Los Angeles, California. Mean counts were 58.7, 102.9, 98.6, and 80.8 X 10(6)/mL (medians 53.5, 88.5, 81.8, and 64.8 X 10(6)/mL) in Missouri, New York, Minnesota, and California, respectively. The total number of motile sperm was also lower in Missouri than in other centers: 113, 196, 201, and 162 X 10(6) in Missouri, New York, Minnesota, and California, respectively. Semen volume and the percent morphologically normal sperm did not differ appreciably among centers. These between-center differences remained significant in multivariate models that controlled for abstinence time, semen analysis time, age, race, smoking, history of sexually transmitted disease, and recent fever (all p-values < 0.01). Confounding factors and differences in study methods are unlikely to account for the lower semen quality seen in this mid-Missouri population. These data suggest that sperm concentration and motility may be reduced in semirural and agricultural areas relative to more urban and less agriculturally exposed areas.

A study by Nelson and Bunge (1974), noting poor semen quality in fertile men from Iowa City, Iowa, relative to men from New York, concluded, Confirmation of our findings would imply that some unknown factor has caused a decrease in male fertility potential as measured by semen analysis.Although the question of a possible decline in semen quality has been widely studied (Carlsen et al. 1992;Swan et al. 1997), before 2003 no other study included a population drawn from an agrarian environment similar to that of Iowa City to confirm or refute this conjecture. Earlier this year we reported results from the Study for Future Families (SFF), a multicenter study of semen quality in fertile men that included men from mid-Missouri, an area comparable demographically and agriculturally with Iowa City (Swan et al. 2003). Iowa City, Iowa, like Columbia, Missouri, has more than 50% of county acreage in farms, and both are located in counties in which pesticide use is high (U.S. Census Bureau 2001).In SFF we found, as had Nelson and Bunge (1974), reduced sperm concentration and motility in men from a U.S. agrarian area (Columbia, MO) relative to men from U.S. urban centers: Los Angeles, California; Minneapolis, Minnesota; and New York, New York. Unlike earlier studies, tight quality control and standardization of all study methods made it unlikely that the variation in semen quality we observed was attributable to differences in laboratory or recruitment methods. We examined multiple potential confounders, and results were largely unchanged after statistical adjustment for these factors. Therefore, we sought to identify environmental agents associated with these between-center differences in semen quality. We hypothesized that pesticides used widely in mid-Missouri, and rarely in urban areas, might have contributed to the poor semen quality seen in men from midMissouri, and perhaps shed light on the finding of Nelson and Bunge (1974). In this article, we follow common use and apply the term "pesticide" not only to insecticides but also to a variety of other agricultural chemicals, including herbicides, fungicides, and various other pest control substances [U.S. Environmental Protection Agency (U.S. EPA) 1997].It is well known that exposure to pesticides at occupational levels can adversely affect semen quality. In the late 1970s the nematocide dibromochloropropane affected more than 26,000 plantation workers in 12 countries; 64% had low sperm concentrations and 28% were involuntarily childless (Goldsmith 1997;Slutsky et al. 1999;Thrupp 1991). The chlorinated hydrocarbon pesticide chlordecone (kepone) was withdrawn in 1975 because of oligozoospermia and decreased motility resulting from occupational exposures (Faroon et al. 1995). Ethylene dibromide was an active component of approximately 100 pesticides. Its use was severely restricted in 1984 because of reduced sperm counts and semen volume in exposed workers (Schrader et al. 1988;Whorton 1981). More recently, a small study of herbicide sprayers in Argentina showed decreased ...

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All funding sources were non-profitable and sponsors of this study played no role in the study design, in data collection, analysis, or interpretation, or in the writing of the article. The authors have no conflicts of interest.