P>Khashan AS, Kenny LC, McNamee R, Mortensen PB, Pedersen MG, McCarthy FP, Henriksen TB. Undiagnosed coeliac disease in a father does not influence birthweight and preterm birth. Paediatric and Perinatal Epidemiology 2010.There is conflicting evidence regarding the effect of coeliac disease (CD) in the father on birthweight and preterm birth. We investigated the association between paternal CD and birthweight and preterm birth. Medical records of all singleton live-born children in Denmark between 1 January 1979 and 31 December 2004 were linked to information about parents' diseases. Fathers who were diagnosed with CD were then identified. Fathers with CD were considered treated if they were diagnosed before pregnancy and untreated if they were diagnosed after the date of conception. The outcome measures were: birthweight, small-for-gestational age (birthweight < 10th centile for gestational age) and preterm birth (< 37 weeks). We compared the offspring of men without CD (n = 1 472 352) and offspring of those with CD [untreated (n = 138) and treated (n = 473)].There was no significant association between untreated CD in the father and birthweight (adjusted mean difference = -3 g; [95% CI -46, 40]) or preterm birth (adjusted odds ratio (OR) = 0.86, [95% CI 0.53, 1.37]) (compared with no CD). There was some evidence for an association between treated paternal CD and birthweight (adjusted mean difference = -81 g; [95% CI -161, -3]), but not preterm birth (adjusted OR = 1.76, [95% CI 0.95, 3.26]). Untreated paternal CD was not associated with an increased risk of reduced birthweight, or of preterm birth. There was some evidence that diagnosis and presumed treatment of paternal CD with a gluten-free diet is associated with reduced birthweight.