Researchers say the results suggest that the hormonal changes associated with pregnancy and birth-control use may be associated with a short-term reduction in MS risk, while the drop in estrogen after delivery may increase the risk of the disease.
They say that estrogen affects the body's immune response, and, therefore, may also affect the development of multiple sclerosis. The disease is believed to be the result of an abnormal immune system response; nerves are attacked and cause the symptoms of the disease.
Estrogen May Affect MS Risk
In the study, which appears in the Archives of Neurology, researchers looked at whether use of birth control pills or pregnancy in the last three years was associated with the risk of MS in a group of more than 106 women in Great Britain who were diagnosed with multiple sclerosis from 1993 to 2000.
Researchers compared the women with MS to more than 1,000 similar women without MS and found the risk of multiple sclerosis was 40% lower among women taking birth control pills compared with nonusers.
The study also showed that the risk of MS was slightly lower during pregnancy but nearly three times higher in the six months following pregnancy.
Researchers say the results suggest that high levels of estrogen -- such as during birth-control use and during pregnancy -- may delay or prevent multiple sclerosis.
The findings are also in line with previous studies in animals that have shown birth control pills, which contain estrogen, delayed the start of and eased the symptoms of MS.