A new study finds that women who give birth may have a lower risk of developing rheumatoid arthritis than women who remain childless, but the potential protective effect seems to fade over the years. The findings, led by Dr. Katherine Guthrie of the Clinical Research and Public Health Sciences divisions, were published in the March 22 online edition of the journal Arthritis & Rheumatism.
RA is an autoimmune disorder that causes inflammation, pain and progressive joint damage. It is more common in women than men, and frequently develops during the childbearing years.
Some studies have suggested that pregnancy may lower a woman's risk of developing RA. It is theorized that fetal cells transmitted to the mother during pregnancy help lower RA risk.
For the current study, Guthrie, along with Dr. Linda Voigt of the Public Health Sciences Division, the Clinical Research Division’s Dr. Lee Nelson, and University of Washington colleagues, examined the pregnancy histories of 310 women newly diagnosed with RA and 1,418 women without the disease.
Overall, women who had had at least one child were 39 percent less likely to have RA than women who had never been pregnant, with factors like oral contraceptive use—previously linked to lower RA risk—taken into account.
The researchers found the protective relationship of pregnancy grew weaker over time. Women who had had their last child within the past five years were 71 percent less likely than childless women to have RA, whereas the risk reduction was 24 percent among women who had last given birth more than 15 years ago. The authors believe the diminished protection might be due to the “natural aging” of the fetal cells, and possibly also due to the aging of the woman's immune system.
The National Institute of Child Health and Human Development and the National Institutes of Health funded the study.