MONDAY, June 30 (HealthDay News) -- The risk of rheumatoid arthritis is twice as high in women who had a heavy birth weight (more than 10 pounds) than those with an average birth weight (7 to 8.5 lbs), a new study finds.

Researchers at the Hospital for Special Surgery, New York City, analyzed data from more than 87,000 women who took part in the U.S. Nurses' Health Study between 1976 and 2002. The women were aged 30 to 55 at the start of the study.

During the study period, 619 women were diagnosed with rheumatoid arthritis. Those with heavy birth weights were more likely to develop rheumatoid arthritis than those with average birth weights. This association held true even after the researchers took into account factors likely to influence birth weight, such as parental smoking, socioeconomic status, maternal diabetes, age at first period, use of oral contraceptives or HRT, breast-feeding and weight.

There is no obvious biological explanation for the finding, said the researchers. But they noted adults with rheumatoid arthritis have abnormal hormone regulation and this process may be triggered while in the womb.

The study, published in the current issue of the Annals of Rheumatic Diseases, supports the fetal origin of disease theory, which states that certain conditions and diseases in adulthood are programmed by factors during pregnancy.

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