Abstract
Higher parental age at childbearing has generated much attention as a potential risk factor for birth disorders; however, previous research findings are mixed. Existing studies have exploited variation in parental age across families, which is problematic because families differ not only in parental age but also in genetic and environmental factors. To isolate the effects of parental age, holding many genetic and environmental factors constant, we exploit the variation in parental age within families and compare outcomes for full siblings. The study data were retrieved from the Medical Birth Registry of Norway, which covers the entire population of births in Norway over an extended period (totaling 1.2 million births). Using variation in parental age when siblings were born, we find large and convex effects of increased parental age on the increased risk of birth disorders. To facilitate comparison with the existing literature, we also estimate the effects of parental age using variation in parental age across families and find that the effects are substantially weaker. We conclude that the existing literature may have underestimated the negative effects of parental aging on adverse offspring outcomes.
Highlights
Parental age at childbearing has increased across the Western world over the last several decades and generated much attention as a potential risk factor for adverse offspring outcomes
We report the results for low birth weight, very low birth weight, preterm birth, and low Appearance, Pulse, Grimace, Activity, and Respiration (APGAR) score
Using data covering all births in Norway over 32 years and employing a sibling design, we found that increased parental age is strongly associated with the increased risk of offspring birth defects and stillbirth
Summary
Parental age at childbearing has increased across the Western world over the last several decades and generated much attention as a potential risk factor for adverse offspring outcomes These include stillbirth [1], low birth weight [29], birth defects [18, 21, 34], preterm birth [11, 36], suicide risk [5], schizophrenia, and autism [28]. Existing literature (cited in the third paragraph) have typically attempted to identify the independent effects of mothers’ age and fathers’age on offspring outcomes This is not feasible with a standard sibling design, as the ages of the mother and father are perfectly collinear. The extant literature, using cohort or case–control designs, has generally found a higher risk of stillbirth with advanced parental age [20]
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