Interpreting trends in fecundity over time

BMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39463.522708.80 (Published 14 February 2008) Cite this as: BMJ 2008;336:339
  1. Jens Peter Ellekilde Bonde, professor of occupational medicine1,
  2. Jørn Olsen, professor of epidemiology2
  1. 1Department of Occupational Medicine, Aarhus University Hospital, DK-8000 Aarhus, Denmark
  2. 2Department of Epidemiology, University of California, 90095-1772 Los Angeles, USA
  1. jpbon@as.aaa.dk

    Is complicated by the lack of direct markers

    Infertility is a common problem in affluent societies. It affects around 15% of couples trying to conceive, although not all seek medical help.1 In some countries, up to 6% of children are conceived through assisted reproductive techniques.2 Many young men have sperm counts that fall short of the limit known to be associated with reduced fecundity.3 It is still unclear whether the past decades have seen a substantial change in the fertility of couples in general or in the fertility of men in particular.4

    The few studies that have examined changes in fecundity over time (or menstrual cycles)—from discontinuation of contraception to pregnancy—show conflicting results.5 Fertility in couples is determined by social, behavioural, and biological factors that cannot be reliably ascertained in studies based on retrospectively …

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