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. In terms of environmental factors, few risk factors are well established, and, in practice, rheumatoid arthritis cannot be attributed to any specific exposure. Descriptive studies imply a birth cohort effect in the incidence of rheumatoid arthritis. 4 We assessed perinatal characteristics in relation to the risk of adult rheumatoid arthritis and observed associations with several perinatal exposures, including high birth weight and low frequency of breast feeding.