Background: Parental age and birth order as risk factors for childhood type 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 between cases and controls, the data were stratified by birth order. For each stratum, odds ratios and their 95% confidence intervals were calculated to assess risks related to the mother's age. The homogeneity of 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 age was found to be a risk factor for type 1 DM. An increase in the mother's age by one year increases the risk of the child being affected by type 1 DM 1.07 times, and children born as the nth in the family are 1.59 times less exposed to the same risk than those born as the (n-1)th.
Conclusions: Children of different birth order have different risks of being affected by type 1 DM. Increased maternal age at the time of delivery is a risk factor for type 1 DM in Upper Silesia, Poland. To avoid bias in estimating risks, the mother's age and child's sequence number should be analyzed jointly.