Birth weight, sex, and celiac disease: a nationwide twin study

OBJECTIVE: Earlier research suggests that birth weight may be associated with celiac disease (CD), but the direction of association has been unclear potentially due to confounding effect from genetic and intrafamilial factors. Through within-twin analyses, we aimed to minimize confounding effects such as twins that share genetic and early environmental exposures. MATERIALS AND METHODS: Using the Swedish Twin Registry, we examined the birth weight of 146,830 twins according to the CD status. CD was defined as having villous atrophy according to a small intestinal biopsy reports. RESULTS: The prevalence of diagnosed CD was 0.5% (n=669), and we included 407 discordant pairs of CD–non-CD twins. Comparing the 669 CD patients with non-CD twins, the association between birth weight and future CD was not statistically significant (odds ratio [OR] per 1000 g increase in birth weight: 1.16; 95% confidence interval [CI]=0.97–1.38). In males, the association was positive and statistically significant (OR=1.50; 95% CI=1.11–2.02). However, the association was not significant in within-pair analyses for both dizygotic and monozygotic twins and for both sexes. CONCLUSION: This population-based study found that in male twins, higher birth weight was associated with higher risk of CD. However, when comparing discordant twin pairs in within-twin pair analyses, there was no statistically significant association between birth weight, intrauterine growth, and future risk of CD.