Interpreting trends in fecundity over time

doi:10.1136/bmj.39463.522708.80

BMJ 2008;336:339-340 (16 February), doi:10.1136/bmj.39463.522708.80

Editorials

Interpreting trends in fecundity over time

Is complicated by the lack of direct markers

The first 150 words of the full text of this article appear below.

Infertility is a common problem in affluent societies. It affectsaround 15% of couples trying to conceive, although not all seekmedical help.¹ In some countries, up to 6% of children are conceivedthrough assisted reproductive techniques.² Many young men havesperm counts that fall short of the limit known to be associatedwith reduced fecundity.³ It is still unclear whether the pastdecades have seen a substantial change in the fertility of couplesin general or in the fertility of men in particular.⁴

The few studies that have examined changes in fecundity overtime (or menstrual cycles)—from discontinuation of contraceptionto pregnancy—show conflicting results.⁵ Fertility in couplesis determined by social, behavioural, and biological factorsthat cannot be reliably ascertained in studies based on retrospectivelycollected data. Therefore, we will never know if biologicalfertility has changed.⁵ Findings of numerous studies of seculartrends in sperm counts are far . . . [Full text of this article]

Jens Peter Ellekilde Bonde, professor of occupational medicine¹, Jørn Olsen, professor of epidemiology²

¹ Department of Occupational Medicine, Aarhus University Hospital, DK-8000 Aarhus, Denmark, ² Department of Epidemiology, University of California, 90095-1772 Los Angeles, USA

jpbon@as.aaa.dk