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Objective: Studies of the importance of perinatal factors for the development of irritable bowel syndrome (IBS) are sparse. We conducted a large national cohort study to examine perinatal and familial risk factors for IBS. Material and methods: A national cohort of 1,963,685 persons who were born in Sweden in 1973-1992 (identified from the Swedish Birth Registry) were followed up for adult (18 years and older) IBS incidence in the Swedish Patient Register through 2010 (maximum age 38 years). There were 24,633 IBS cases in 46,784,296 person-years of follow-up. Results: After adjusting for potential confounders, significant risk factors for IBS included caesarean (HR = 1.10, 95% confidence interval [CI] 1.05-1.11, p < .001), low birth weight (<2500g) (HR = 1.11, 95%CI 1.01-1.22, p = .02), being second in birth order (HR = 1.04, 95%CI 1.01-1.08, p = .01), foetal growth ≥1 SD (HR = 1.06, 95%CI 1.00-1.11, p = .05), young maternal age (<20 years) (HR= 1.09, 95%CI 1.02-1.17, p = .02), maternal marital status (divorced/widowed) (HR = 1.12, 95%CI 1.08-1.17, p < .001), maternal education of 10-11 years (HR = 1.04, 95%CI 1.01-1.08, p = .01), maternal education of 12-14 years (HR = 1.06, 95%CI 1.01-1.11, p = .03), parental history of IBS (HR = 1.54, 95%CI 1.42-1.66, p < .001), parental history of anxiety (HR = 1.21, 95%CI 1.17-1.26, p < .001) and parental history of depression (HR = 1.09, 95%CI 1.02-1.17, p = .02). Protective factors were male sex (HR = 0.36, 95%CI 0.35-0.37, p < .001) and old maternal at delivery (≥35 years) (HR = 0.95, 95%CI 0.90-1.00, p = .03). Conclusions: In this large cohort study, several perinatal and familial factors were associated with an increased risk of IBS independently, suggesting that perinatal and familial factors may play an important long-term role in the aetiology of IBS. [ABSTRACT FROM AUTHOR]

Objectives: IBS aggregates in families, but the familial risk of IBS has only been determined in first-degree relatives and spouses. This nationwide study aimed to determine the familial risk of IBS in first-degree, second-degree, and third-degree relatives and spouses of affected individuals in order to estimate the relative influences of genes and shared family environment., Methods: We performed a case-cohort study. The Swedish Multigeneration Register was linked to the Hospital Discharge Register for the period 1987-2010 and the Swedish Outpatient Care Register for 2001-2010. ORs for IBS were calculated for relatives of individuals who had been diagnosed with IBS compared with relatives of individuals unaffected by IBS as the reference group. ORs were also determined for IBS cases diagnosed in primary healthcare in four Swedish counties (2001-2007)., Results: The ORs for IBS were 1.75 in siblings (95% CI 1.63 to 1.89), 1.82 in offspring (1.67 to 1.97), 1.90 in parents (1.76 to 2.05), 1.10 in maternal half-siblings (0.88 to 1.39), 1.78 in paternal half-siblings (1.48 to 2.15), 1.27 in nieces/nephews (1.18 to 1.38), 1.11 in cousins (1.04 to 1.18), and 1.51 in spouses (1.24 to 1.84) of probands diagnosed with IBS. The OR for probands diagnosed in primary healthcare was 1.82 in siblings (1.52 to 2.18), and 1.82 in offspring (1.49 to 2.21)., Conclusions: The increased IBS risk among first-degree relatives and also second-degree and third-degree relatives indicates a genetic component of the familial clustering of IBS. However, a non-genetic contribution is also suggested by the increased risk among spouses., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)