Perinatal characteristics and risk of rheumatoid arthritis
Rheumatoid arthritis is a disease of unknown aetiology. Twin studies indicate the importance of genetic as well as environmental factors. 1 In terms of environmental factors, few risk factors are well established, and, in practice, rheumatoid arthritis cannot be attributed to any specific exposure. 2 Descriptive studies imply a birth cohort effect in the incidence of rheumatoid arthritis. 3 4 We a