* Corrected for seasonal variation at month of sampling. aOR; adjusted odds ratio, OR; odds ratio, CI; confidence interval. The primary analysis used the modelled mean concentration of 25-hydroxyvitamin D across all available samples, predicted from mixed effects random intercept model. P for trend = 0.26. Maternal samples from week 18: cases, n = 386; controls n = 529. P for trend 0.78 Maternal samples after delivery: cases, n = 374; controls, n = 522. P for trend 0.50. Samples from cord blood: cases, n = 397, controls, n = 547. P for trend 0.60. Odds ratios adjusted for sex, attained age, maternal celiac disease, non-HLA genetic risk score and HLA haplotype.