If you’re a woman who has experienced the miracle of childbirth, you probably feel like that “miracle” left you with some less than heavenly after-effects: extra pounds you just can’t shed, stretch marks, postpartum depression, maybe even bladder control problems. But here’s one thing you can be thankful for: A new study found women who’ve given birth to at least one child are less likely to be diagnosed with rheumatoid arthritis than those who haven’t.

Rheumatoid arthritis… also called ‘R-A’… causes swollen, painful joints and sometimes affects organs. It can lead to deterioration of bones and cartilage, as well as general fatigue and fevers. The national Centers for Disease Control and Prevention says about 1.3 million American adults suffer from RA. It’s most common in women ages 40 to 60, and is likely caused by a genetic predisposition to the disease that may be activated by infections.

Researchers writing in the journal Arthritis and Rheumatism say women who’ve given birth are about 40 percent less likely to be diagnosed with RA than those who’ve never had kids. But the protection seems to dissipate over time, with women who’d most recently given birth showing the least risk of the diagnosis. Older moms… those over 45… didn’t see much of an advantage, regardless of when their kids were born. And women who’ve been pregnant but not given birth didn’t see any benefits.

What reduces the risk for some moms? Transfer of some of the baby’s cells into the mother during pregnancy may have something to do with it. This phenomenon could help protect mom if baby’s cells contain a specific substance that wards off rheumatoid arthritis. These cells might offer less protection the older they become.