Pregnancy may delay the onset of multiple sclerosis (MS) symptoms by more than three years, a study has indicated.
Researchers say the finding has implications for a greater understanding of the causes of MS as well as the potential use of hormone therapy to delay symptoms.
It is estimated that more than 2.5 million people worldwide have the neurological condition, with women four times more likely to have the disease than men.
The study, which used a global database of more than 70,000 MS patients and was run by Monash University in Australia, looked at whether pregnancy can delay the onset of MS, which is very frequently diagnosed in women in their 20s and 30s, though it can develop at any age.
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Dr Vilija Jokubaitis, from the university’s department of neuroscience, studied more than 3,600 women attending four MS clinics in the Czech Republic and Australia, all of whom were enrolled in MSBase – a database of more than 70,000 people with MS in 35 countries.
The study published in the JAMA Neurology journal found women who have been pregnant were diagnosed with their first MS symptoms on average 3.3 years later than women who had never been pregnant.
A similar delay was also observed in women who had carried a baby to term – with onset delayed by an average of 3.4 years.
Dr Jokubaitis suggests pregnancy could reduce the abnormal overactivity of the immune system that causes MS, potentially long term.
She said: “At present, we don’t know exactly how pregnancy slows the development of MS, but we believe that it has to do with alterations made to a woman’s DNA.
“We are now seeking funding opportunities to explore this exciting possibility.”
The study suggests an association between previous pregnancies and childbirths and timing of clinically isolated syndrome onset, but having more pregnancies or childbirths did not appear to be associated with a later onset.
The researchers said further studies are needed to help explain the mechanisms behind the associations between pregnancy and onset of multiple sclerosis.
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Dr Emma Gray, assistant director of research at the MS Society, said: “MS affects over 130,000 of us in the UK, with women ‘of reproductive age’ almost three times more likely to be diagnosed.
“We know many women living with MS experience fewer symptoms while they are pregnant.
“This new study builds further evidence for pregnancy’s protective influence, by showing that having been pregnant is associated with later onset of clinically-isolated syndrome, which can be the first sign of MS.
“The reasons for pregnancy’s positive effect are not fully understood, but it’s thought the answer lies in our immune system – which misbehaves in MS, but is dampened during pregnancy.
“We want to slow, stop and eventually prevent MS, and these findings could help us with that goal. We’re also funding a project at Oxford University to further our understanding – if we can figure out the mechanisms underlying this apparent protective effect of pregnancy, it could lead to new avenues for treatment.”
Q&A: What is the evolutionary benefit of morning sickness during pregnancy?
Morning sickness in pregnancy appears to be unique to humans, and it seems that women with more severe morning sickness have a lower rate of miscarriage. There are two main theories to explain why we might have evolved this.
The first is that the nausea is commonly associated with an aversion to meat and strong tastes, and this might be a way of steering the mother away from foods that might cause food poisoning, especially early in pregnancy when the foetus is most vulnerable.
The second theory is that morning sickness is caused by the hormones secreted by healthy foetuses, which are important for building the placenta in the first trimester. In that case, the nausea is just an unfortunate side effect of these hormones, and the advantage is an indirect one.
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