Birthweight and risk of type 1 diabetes in children and young adults:: a population-based register study

We investigated the association between type 1 diabetes and birthweight by age at disease onset. This population-based case-referent study used data from two nationwide case registers that are linked to the Swedish Medical Birth Registry and cover incident cases of type 1 diabetes in the 0- to 14-year (since 1 July 1977) and 15- to 34-year age groups (since 1 January 1983). Of the cases linked to the Medical Birth Registry, a total of 9,283 cases with onset before 15 years of age was recorded before 1 January 2003, and 1,610 cases were recorded with onset before 30 years of age and born after 1973 (together 95% of eligible cases). Multiple births and babies of diabetic mothers were excluded. Sex-specific birthweight by gestational week is expressed as multiples of the standard deviation (SDS) and adjusted for year of birth, maternal age and parity. Cases with onset before 10 years of age (n=5,792) showed a significant linear trend in odds ratio (OR) by SDS of adjusted birthweight (OR by SDS: 0.062; 95% CI: 0.037-0.086; p < 0.0001), while cases with onset at the age of 10-29 years showed no significant trend (OR by SDS: 0.004; 95% CI: -0.007 to 0.0014; p=0.22). The association between type 1 diabetes risk and birthweight seems to be limited to cases with disease onset in younger years.