Background: Parental age and birth order as risk factors for childhoodtype 1 diabetes mellitus were investigated using data from the Regional Diabetic Center for Upper Silesia,Poland, in a population-based study of 398 children with type 1 DM aged 0-14 years born between 1979-1996.Material/Methods: Noting differences in the proportions of children of different birth order betweencases and controls, the data were stratified by birth order. For each stratum, odds ratios and their95% confidence intervals were calculated to assess risks related to the mother's age. The homogeneityof the odds ratios related to the mother's age between strata was evaluated by the Mantel-Haenszel method.Risks related to mother's age and birth order were also estimated jointly by multivariable logistic regression.Results: Decreased risk in later children compared with firstborns was noted. Increased maternal agewas found to be a risk factor for type 1 DM. An increase in the mother's age by one year increases therisk of the child being affected by type 1 DM 1.07 times, and children born as the nth in the familyare 1.59 times less exposed to the same risk than those born as the (n-1)th. Conclusions: Children ofdifferent birth order have different risks of being affected by type 1 DM. Increased maternal age atthe time of delivery is a risk factor for type 1 DM in Upper Silesia, Poland. To avoid bias in estimatingrisks, the mother's age and child's sequence number should be analyzed jointly.

Keywords: Risk Factors, Pregnancy, Poland, Odds Ratio, Maternal Age, Infant, Newborn, Adolescent, Diabetes Mellitus, Type 1 - etiology, Child, Preschool, Child, Case-Control Studies, Birth Order