Hyperemesis, gestational hypertensive disorders, pregnancy losses and risk of autoimmune diseases in a Danish population-based cohort.

The risk of some female predominant autoimmune diseases (ADs) has previously been shown to be higher in women who experience hyperemesis, gestational hypertensive disorders and idiopathic pregnancy losses. This study assessed the association between such pregnancy-related experiences and the subsequent risk of female predominant and other ADs. Our study cohort comprised 1.6 million Danish women born since 1955 for whom we had information about hyperemesis, gestational hypertensive disorders and pregnancy losses and subsequent hospital contacts for 31 ADs between 1982 and 2008. Ratios of first hospitalization rates (RRs) with 95% confidence intervals (CIs) were calculated using Poisson regression, adjusting for age, birth cohort, calendar period, marital status and childbirths. During 27.0 million person-years of follow-up 51,732 women were hospitalized with one or more ADs. Overall, compared with women without the specific pregnancy experiences, the risk of any AD was significantly increased for women with hyperemesis (RR = 1.41; 95% CI 1.30-1.51), gestational hypertensive disorders (1.21; 1.16-1.26), spontaneous abortions (1.10; 1.07-1.14), missed abortions (1.09; 1.04-1.13), stillbirths (1.25; 1.12-1.40), ectopic pregnancies (1.08; 1.02-1.14) and induced abortions (1.07; 1.04-1.09). Associations with female predominant ADs (i.e., ADs with a female:male ratio >2:1) were strongest in the first five years after the studied pregnancy experiences, but overall there was little difference between the RRs for groups of female predominant ADs and other ADs. Strong and potentially biological associations were observed for a number of specific ADs; including systemic lupus erythematosus, Graves' disease, type 1 diabetes mellitus and pernicious anemia, and for some specific ADs associations persisted even more than five years after the abnormal pregnancy experience. Abnormal pregnancies are associated with increased risk of certain ADs, possibly because of underlying immunologic or hormonal factors that predispose to both adverse pregnancy experiences and AD development.