Figure 1

 The inclusion of subjects into the study according to current reproductive status and reproductive history in a study among farmers and their wives in the Agricultural Health Study. (1) Couples who currently had been >12 months without using any contraception were included as subfertile (n = 305). For all the others, inclusion was considered on the basis of having at risk time within four years of enrolment. These included (2) those who currently were not at risk of getting pregnant, i.e. pregnant, breast feeding, or using contraception (n = 4820), and (3) those for whom fertility status could not be defined reliably (n = 401).