Secular trends in monitors of reproductive hazard

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Abstract
There is concern that our reproductive systems are exposed to environmental hazards. A number of potential monitors of these hazards have been proposed (reported rates of cryptorchidism, testicular cancer, hypospadias, dizygotic twinning, sperm count, ectopic pregnancy and sex ratios). To discover whether these are monitoring the same hazards, secular movements in these measures are considered here. It is suggested that the secular movements of cryptorchidism and hypospadias are insufficiently reliable to give guidance on the movements of such hazards as cause them. With one possible exception, rates have not moved in parallel and so, in general, they are not monitoring the same hazards. The exception is dizygotic twinning rates and sperm counts which may have a lagged correlation. If this is true, it may be important and throw light on the hitherto unexplained movements of both. The hazards themselves are largely unidentified, but may be presumed to include: (i) the well-publicized rise in environmental oestrogens; (ii) an increasing number of women with suboptimal oestrogens (because of dieting and arduous exercise); and (iii) hormonal consequences of these two opposing trends, e.g. an increasing number of women with suboptimal androgens (possibly accounting for the increasing rates of cryptorchidism and testicular cancer).

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