A prospective study of male factors, fertility, and pregnancy outcomes - ABSTRACT About 15% of American couples experience infertility (time-to-pregnancy >12 months) and more than 20% of couples experience spontaneous abortion (SAB, pregnancy loss <20 weeks' gestation). The prevalence of impaired fecundity has increased over the last decade and studies indicate that sperm counts have been declining over the last four decades. Male factor contributes to 50% of infertility, yet epidemiologic research on predictors of male infertility is scarce and male participation in reproductive health studies has been low. Even less research has explored paternal influences of perinatal and pediatric health outcomes. With funding from the NICHD, we launched Pregnancy Study Online (PRESTO) in June 2013 to assess the feasibility of conducting a web-based preconception cohort study in North America to evaluate dietary, lifestyle, and medical determinants of fecundity. Since June 2013, we have recruited more than 13,000 females and 3,000 of their male partners from the United States and Canada. In this cohort, we have shown that male exposures, such as male sleep and sugar-sweetened beverage intake, are strong determinants of fertility. In our NICHD-supported feasibility grant (R21-HD094322), we demonstrated that at-home semen testing is feasible, with 400 men providing at least one semen sample during a 3-year period. Preconception enrollment of men from the general population presents a unique opportunity to examine how male factors influence semen quality, and the extent to which semen quality and selected male factors predict reproductive and perinatal outcomes. We now propose to recruit an additional 2,000 men—including 800 in the semen testing substudy—to assess a broader set of aims: 1) to evaluate the association of selected behavioral factors with poor semen quality, focusing on common but understudied factors for which studies are limited or inconclusive (e.g. poor or inadequate sleep, bicycling, marijuana use, e-cigarette use/vaping, and intake of sugar-sweetened, caffeinated, and alcoholic beverages); 2) to assess the extent to which poor semen quality predicts subfertility, SAB, and adverse perinatal outcomes (shorter gestational length and lower infant birthweight); and 3) to evaluate male factors in relation to risk of SAB and adverse perinatal outcomes, and the extent to which these associations are mediated by semen quality. Importantly, we will assess exposures jointly with female factors to better investigate causal pathways. Increased granularity of sleep and activity exposures will be collected through a pilot aim to examine the feasibility of disseminating FitBit actigraphs to a subset of 100 participants. We have already shown that appreciable numbers of men are willing to enroll in our preconception cohort study, that men are willing to perform at-home semen testing, and that the semen data are within the range expected for the general population. The use of an innovative and cost-effective semen testing method, the prospective study design, the established infrastructure of PRESTO, and the comprehensive collection of risk factor data in both male and female partners are added strengths. Results from the proposed study will have important public health and clinical implications for male reproductive health.