Decreased fertility in Britain compared with Finland

There has been much interest in the apparent decrease in semen quality. Because the evidence for such a decrease is open to criticism, a different type of evidence is needed. Finland seems to have escaped this decrease, as well as other disorders of the male reproductive tract, notably testicular cancer. If there has been a true decrease, the implications for fertility are unknown.

The most sensitive functional measure of fertility is time to pregnancy (TTP); this can be studied retrospectively at group level with a high degree of validity. To test the hypothesis that Finnish men are more fertile than British men, TTP distributions from published Finnish studies and data from Britain were compared. Two comparisons were made: a pair of antenatal studies, and a pair of cross-sectional studies.

In both comparisons, fertility was statistically significantly greater in Finland than in Britain. The findings did not seem to be due to methodological problems; in particular, the results could not be attributed to differences in frequency of intercourse, since this would have had the opposite effect on sperm concentration and on TTP.

The previously reported difference in sperm counts between Finland and elsewhere in northwest Europe (including Britain) is probably not artefactual, suggesting that the reported world-wide decline in semen quality is also real. Reasons for the "Finnish exception" may include maternal smoking, which used to be lower in Finnish women than elsewhere, and which might affect developing make offspring.