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Abstract

<p><strong>Background&nbsp;</strong>Based on existing studies, there is no conclusive evidence as to whether and why paternal age matters for birth outcomes.</p> <p><strong>Methods&nbsp;</strong>We used Finnish Population Registers on 106,652 children born&nbsp;1987-2000. We first document the unadjusted association between paternal age and the risk of low birth weight&nbsp;(&lt;2500g; LBW)and preterm birth&nbsp;(&lt;37 weeks gestation). Second, we investigate whether the unadjusted association is attenuated on adjustment for child&rsquo;s, maternal and parental socio-economic characteristics. Third, by adopting a within-family design which involves comparing children born to the same father at different ages, we additionally adjust for unobserved parental characteristics shared between siblings.</p> <p><strong>Results&nbsp;</strong>The unadjusted results show thatbeing born to a father aged 40+, as opposed to a father 30-34, is associated with an increased risk of LBW of 0.96 percent (95% CI: 0.5%-1.3%) and to a younger father (&lt;25) with a 1 percent (95% CI: 0.6%-1.3%) increased risk. The increased risk at younger paternal ages is halved on adjustment for the child&rsquo;s characteristics and fully attenuated on adjustment for child/parental characteristics. The increased risk at paternal ages 40+ is partially attenuated on adjustment for maternal characteristics (&beta;=0.62%; 95% CI: 0.13%-1.1%). Adjustment for unobserved parental characteristics shared by siblings further attenuates the 40+ coefficient (&beta;=0.4%; 95% CI: -0.5%-1.2%). Results for preterm delivery are similar.</p> <p><strong>Conclusions </strong>The results underscore the importance of considering paternal age as a potential risk factor for adverse birth outcomes and of expanding research on its role and the mechanisms linking it to birth outcomes.</p>