Maternal and paternal age at delivery, birth order, and risk of childhood onset type 1 diabetes: population based cohort

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Abstract
Objective: To estimate the associations of maternal and paternal age at delivery and of birth order with the risk of childhood onset type 1 diabetes. Design: Cohort study by record linkage of the medical birth registry and the national childhood diabetes registry in Norway. Setting: Norway. Subjects: All live births in Norway between 1974 and 1998 (1.4 million people) were followed for a maximum of 15 years, contributing 8.2 million person years of observation during 1989-98. 1824 cases of type 1 diabetes diagnosed between 1989 and 1998 were identified. Main outcome measures: Incidence of type 1 diabetes. Results: There was no association between maternal age at delivery and type 1 diabetes among firstborn children, but among fourthborn children there was a 43.2% increase in incidence of diabetes for each five year increase in maternal age (95% confidence interval 6.4% to 92.6%). Each increase in birth order was associated with a 17.9% reduction in incidence (3.2% to 30.4%) when maternal age was 20-24 years, but the association was weaker when maternal age was 30 years or more. Paternal age was not associated with type 1 diabetes after maternal age was adjusted for. Conclusions: Intrauterine factors and early life environment may influence the risk of type 1 diabetes. The relation of maternal age and birth order to risk of type 1 diabetes is complex. What is already known on this topic Maternal age at birth is positively associated with risk of childhood onset type 1 diabetes Studies of the effect of birth order on risk of type 1 diabetes have given inconsistent results What does this study add? In a national cohort, risk of diabetes in firstborn children was not associated with maternal age Increasing maternal age was a risk factor in children born second or later The strength of the association increased with increasing birth order