Does pregnancy provide vaccine-like protection against rheumatoid arthritis?
Version of Record online: 22 MAR 2010
Copyright © 2010 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 62, Issue 7, pages 1842–1848, July 2010
How to Cite
Guthrie, K. A., Dugowson, C. E., Voigt, L. F., Koepsell, T. D. and Nelson, J. L. (2010), Does pregnancy provide vaccine-like protection against rheumatoid arthritis?. Arthritis & Rheumatism, 62: 1842–1848. doi: 10.1002/art.27459
- Issue online: 29 JUN 2010
- Version of Record online: 22 MAR 2010
- Manuscript Accepted: 12 MAR 2010
- Manuscript Received: 14 AUG 2009
- National Institute of Child Health and Human Development. Grant Number: N01-HD-62914
- NIH. Grant Numbers: AI-45659, AI-41721
Previous studies have evaluated the correlation between rheumatoid arthritis (RA) risk and pregnancy history, with conflicting results. Fetal cells acquired during pregnancy provide a potential explanation for modulation of RA risk by pregnancy. The present study was undertaken to examine the effect of parity on RA risk.
We examined parity and RA risk using results from a population-based prospective study in Seattle, Washington and the surrounding area and compared women who were recently diagnosed as having RA (n = 310) with controls (n = 1,418). We also evaluated the distribution of parity in cases according to HLA genotype.
We found a significant reduction of RA risk associated with parity (relative risk [RR] 0.61 [95% confidence interval 0.43–0.86], P = 0.005). RA risk reduction in parous women was strongest among those who were younger. Most striking was that RA risk reduction correlated with the time that had elapsed since the last time a woman had given birth. RA risk was lowest among women whose last birth occurred 1–5 years previously (RR 0.29), with risk reduction lessening progressively as the time since the last birth increased (for those 5–15 years since last birth, RR 0.51; for those >15 years, RR 0.76), compared with nulliparous women (P for trend = 0.007). No correlation was observed between RA risk and either age at the time a woman first gave birth or a woman's total number of births. Among cases with the highest genetic risk of RA (i.e., those with 2 copies of RA-associated HLA alleles), a significant underrepresentation of parous women versus nulliparous women was observed (P = 0.02).
In the present study, there was a significantly lower risk of RA in parous women that was strongly correlated with the time elapsed since a woman had last given birth. While the explanation for our findings is not known, HLA-disparate fetal microchimerism can persist many years after a birth and could confer temporary protection against RA.