Does pregnancy provide vaccine-like protection against rheumatoid arthritis?

Arthritis Rheum. 2010 Jul;62(7):1842-8. doi: 10.1002/art.27459.


Objective: 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.

Methods: 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.

Results: 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).

Conclusion: 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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adolescent
  • Adult
  • Arthritis, Rheumatoid / epidemiology
  • Arthritis, Rheumatoid / immunology
  • Arthritis, Rheumatoid / prevention & control*
  • Case-Control Studies
  • Chimerism
  • Female
  • HLA Antigens / genetics
  • HLA Antigens / immunology
  • Humans
  • Middle Aged
  • Parity / genetics
  • Parity / immunology*
  • Pregnancy / immunology*
  • Pregnancy Complications / epidemiology
  • Pregnancy Complications / immunology
  • Pregnancy Complications / prevention & control*
  • Prospective Studies
  • Risk Factors
  • Time Factors
  • Vaccination*
  • Washington / epidemiology
  • Young Adult


  • HLA Antigens