And the "impaired fecundity" category contains findings that may have a bearing on the are-young-men-more-infertile-than-their-fathers question. In the United States, "impaired fecundity" among women has seen, over several decades, a steady rise. And while much attention has focused on older women, the most striking rise between 1982 and 1995 took place among women under 25. In that period, impaired fecundity in women under 25 rose by 42 percent, from 4.3 percent of women to 6.1 percent. Recently published data from 2002 show a continued rise in impaired fecundity among the youngest age cohort.
In a 1999 letter to Family Planning Perspectives, Swan sensibly proposed "that the role of the male be considered in this equation." If sperm counts drop each year, then the youngest men will be most acutely affected, and these will be the men who are having trouble impregnating their partners. In 2002, Danish researchers published an opinion piece in Human Reproduction noting that teen pregnancy rates (already much lower than in the United States) fell steadily in Denmark between 1985 and 1999. Unlike in the United States, in Denmark there have been no changes in outreach efforts to encourage responsible behavior in teens: no abstinence campaigns, no big new push for condom distribution. Wider social trends notwithstanding, they note that "it seems reasonable also to consider widespread poor semen quality among men as a potential contributing factor to low fertility rates among teenagers."
Among other things, the sperm-count debate reminds us that we should not be smug about the success of teen-pregnancy prevention efforts. We may not want today's teenagers to become pregnant now, but we certainly want them to become pregnant in the future, providing they want to be. If nothing else, the sperm-count hypothesis shows that when it comes to teenagers and sexual behavior, there's always something new to worry about.