8.5 million people in the U.S. have an autoimmune disease where their immune system is attacking some part or parts of their own body. 6.7 million, almost 80 percent, are female. Researchers have discovered that pregnancy may be a triggering factor. “During pregnancy a mother and fetus exchange body cells that can persist in one or the other’s circulation for years or even decades after birth.” When the molecules that identify cells as being the mother’s or the child’s are too similar, the immune system can get confused and attack the wrong cells postpartum. Type 1 diabetes, lupus, and rheumatoid arthritis are some examples of autoimmune disorders. Scientists have realized they need to study these as a group.