It is hypothesized that the well-evidenced global decline in reproductive health may, together with behavioral factors, be contributing to the world’s declining fertility and to a soon-expected decreasing global population. Time to pregnancy (TTP), defined as the time to success to conceive under unprotected intercourse, is a commonly used population measure of fecundity, defined as an individual’s capacity to reproduce irrespective of pregnancy intentions. Age is the most significant factor for fecundity in men and women, whereas environmental and lifestyle factors explain around 70% of impaired fecundity in women and 95% in men. Lower semen quality and infertility have been linked to both health and mortality; however, because of the lack of comparable reproductive health measures in women, the data are less clear and long-term studies are limited.

This prospective cohort study of women aimed to evaluate whether fecundity, measured as TTP, is associated with overall and cause-specific mortality. Reproductive data, including TTP and medical, occupational, and lifestyle information, were obtained from the Odense Pregnancy Cohort, which includes all women who attended prophylactic antenatal care between 1973 and 1987 at Odense University Hospital in Denmark. Only first-time pregnancies were included in this study. The Danish Civil Register of Causes of Death was used to determine mortality data, and the final data set included information on deaths for mothers and fathers up to January 2018 and December 2016, respectively. Fecundity was characterized as follows by how long it took those who wanted a pregnancy to obtain it: <12 months, ≥12 months, “not planned,” and “not available.” Analyses were adjusted for age at first attempt to become pregnant, year of birth, socioeconomic status, mother’s smoking status during pregnancy, and mother’s body mass index. The relative associations between TTP and death or cause of death were addressed using Cox regression.