Commenting on infertility, experts from the Aarhus University Hospital, Denmark and the University of California observe that infertility is a common problem in affluent societies, and it affects some 15% of couples who are trying to conceive.

Assisted reproductive methods are used in some countries to conceive up to 6% of children. But fertility is determined by social, behavioral and biological factors, say the authors, which could make studies based on retrospectively collected data unreliable. These cultural and social norms may mask more subtle biological changes in the population, and representative health surveys should include fecundity.

Fecundity is expected to decline over time, the study’s authors predict, because with the availability of assisted conception subfertile couples may have as many children as fertile couples. Genetic factors linked to infertility will become more prevalent in the future. Meanwhile, dealing with the causes of subfecundity, say the authors, is the best way to fight infertility, and neglected research should be undertaken without delay.