Background Female sex and older age are known risk factors for rheumatoid arthritis (RA). The disease is however heterogeneous, and a common division occurs between the presence/absence of autoantibodies to citrullinated peptide antigens (ACPA) where ACPA-positive disease generally has a worse outcome. In a recent study we reported that parous women of reproductive age (18 to 44 years at diagnosis) had an increased risk of ACPA-negative, but not of ACPA-positive RA, and that this association was stronger closer to partum. There are diverging results regarding the effect of parity on the severity of RA [2-4]
Objectives To explore the impact of parity on disease severity of ACPA-positive/-negative RA.
Methods We studied female RA cases aged 18-70, who participated in the Epidemiological Investigation of Rheumatoid arthritis, EIRA, a population-based case-control study from the middle and southern parts of Sweden. All patients were diagnosed by a rheumatologist, included within 1 year of diagnosis and fulfilled the American Collage of Rheumatology 1987 criteria for RA. Information on disease severity (Health Assessment Questionnaire, HAQ and disease activity score 28, DAS28) was retrieved from the Swedish Rheumatology Register, SRQ at inclusion, 3, 6, 12 and 24 months after diagnosis. Mixed models for repeated measurements over time were used to take account of the variation at different time point at individual level and to compare mean DAS28 and HAQ-scores over time. ANCOVA analysis was used to compare mean differences of clinical outcome measures at all time points. All analyses were adjusted for age.
Results A total of 1237 female cases (mean age 51 years, 65% ACPA positive) with complete information, were included in the study. In all, 82% had ever given birth to a child before diagnosis. In the mixed models analysis, parous women, aged 18-44, who had an ACPA-negative disease, had on average 1.17 units higher DAS28 (p= <0.001) and 0.43 units higher HAQ score (p= <0.001) compared to nulliparous women during the follow up time, adjusted for age. Results were similar after individual adjustment for smoking, living area or level of education. The ANCOVA analysis for different time points revealed an association between parity and higher DAS28 and HAQ levels in the ACPA-negative reproductive age group (18-44) at all time points, except at baseline. In post-reproductive ACPA negative women (aged 45-70), parity was associated with lower DAS28 (p≤0.001) and HAQ (p=0.001) at baseline, but not at later time points. No associations were observed in ACPA-positive women.
Conclusions Parity influenced the severity of ACPA-negative RA, where parous women who developed RA during their reproductive years had on average higher DAS 28 and HAQ score than nulliparous women during the first 24 months. Parity was not associated with the severity of ACPA-positive disease; neither at younger nor at older ages.
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Disclosure of Interest None declared