BMJ 1994;309:959 (8 October)

Letters

No secular decline in fecundity has occurred in Sweden

EDITOR, - Stephen Farrow's editorial highlights the important epidemiological issue of whether human fertility is threatened by environmental pollution or occupational exposure.1 The methodological problems in studies of this are well recognised and include the study design, measures of exposure, reproductive and developmental outcomes, interaction, participation, and recall bias.2 How then could we address the hypothesis of a possible secular decline in fertility?

A decline in the twinning rate has been suggested to be related to increased rates of miscarriage and environmental pollution.3 The changed distributions of age and parity of mothers, however, explain the secular decline in the twinning rate from the 19th century until 1960 in Sweden, while the continued decline during the 1960s remains unexplained.4

Time to pregnancy, with live birth as the outcome variable, could be a more valid and consistent measurement for analysis of secular trends in fecundity. We have studied fecundity among Swedish peasant . . . [Full text of this article]


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