The study, published online Wednesday in the journal Neurology, reviewed information on 282 men and women who received a diagnosis of central nervous demyelination. That's a condition that reflects early symptoms of MS but falls short of an actual MS diagnosis. The researchers compared those people to 542 healthy men and women.
They found that women who have been pregnant two or more times had a reduced risk of developing the disease. Women who had five or more pregnancies had one-twentieth the risk of developing MS compared with women who were never pregnant. There was no effect on men regarding their number of offspring and onset of the disease.
Rates of MS have increased over the last several decades. This increase could reflect the fact that women are having fewer children, said the lead author of the study, Anne-Louise Ponsonby of Murdoch Children's Research Institute in Melbourne, Australia.
It's not clear what it is about pregnancy that protects against MS or causes its temporary remission. It's likely that hormones play a role, and studies are under way looking at estrogen as a treatment for the illness. It's also possible that immune changes that take place during pregnancy alter symptoms of the disease as well as the risk of developing it.
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