In line with those studies, a meta-analysis that included 12 studies demonstrated a borderline significant inverse association between parity (versus nulliparity) and RA (RR 0.90, 95% CI 0.79–1.02), and a significant nonlinear inverse relation between parity number and the risk of RA [ 95 ].
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The sentences
There was no association overall, but in ever-smokers, there was a significant trend towards a reduced risk of RA with a higher MD score.