Giving birth seems to slow the progression of multiple sclerosis (MS), Belgian and Dutch researchers say.
The researchers tracked 330 women with MS for 18 years and found that among those who had children, severe disability took longer to develop.
Writing in the Journal of Neurology, Neurosurgery and Psychiatry, they say previous studies have suggested a worsening of MS just after birth.
But the MS Society said the study was flawed and further research was needed.
MS is a long-term inflammatory condition of the central nervous system.
It affects the transfer of messages from the nervous system to the rest of the body.
Women are twice as likely to develop MS as men and many of the new cases will be among women of childbearing age.
The researchers from Belgium and the Netherlands said all the women had been referred to one specialist centre and had had their first symptoms from the ages of 22 to almost 38.
Nearly a quarter of the women (24%) were childless; 170 had given birth before their symptoms developed (52%); 61 had their children after their symptoms developed (18%); and 19 had had children both before and afterwards (6%).
'Speed of progression'
The researchers used the Kurtzke Expanded Disability Status Scale (EDSS) which runs from one to 10, where 10 is death from MS and six is when an individual needs a cane, a crutch or a brace to walk 100m.
After an average of 18 years living with MS, over half the women (55%) were categorised as EDSS six.
They found that both the likelihood and speed of progression were affected by childbirth.
Women who had given birth to one or more children at any point before or after the start of MS symptoms were 34% less likely to progress to EDSS six than childless women.
Women whose children had been born after their MS began were 39% less likely to progress to EDSS six than women who had not had children.
They said this held true even after taking account of the age at which symptoms began.
Women who had no children after their MS symptoms started progressed to EDSS six within 13 to 15 years on average.
But women who did have children took an average of 22 to 23 years to reach this stage.
Dr Maria D'hooghe, from the National MS Centre in Melsbroek, Belgium, which co-ordinated the study, said it had shown for the first time the long-term effects of having a baby if you have MS.
She said: "It's possible that the hormones released in pregnancy are having a beneficial effect on the immune system.
"Certainly, animal studies show that pregnancy can lead to less damage in their brains.
"The other possibility is that it is lifestyle changes caused by having a baby that are delaying the effects of MS perhaps through increased activity or changes in the way we deal with stress."
But Dr Susan Kohlhaas, research communications officer for the MS Society, said it was a small study and they had not taken account of the fact that women with more severe MS may choose not to get pregnant because they are worried about a relapse or about taking care of a baby during a relapse.
She said: "It is difficult to form any meaningful conclusions from this research given the small size of the study and its flaws, but further studies will hopefully clarify the effects of pregnancy in women with MS."
Article taken from : http://news.bbc.co.uk/1/hi/health/8374009.stm