Severe morning sickness could have an hereditary link, a study suggests.
The Norwegian Institute of Public Health found women were three times more likely to have hyperemesis gravidarum if their mother suffered with the condition.
Thousands of women a year experience morning sickness, which strikes before week 22 of a pregnancy and affects up to 2% of women.
It can lead to weight loss, dehydration and deprivation of essential nutrients for both mother and baby.
Babies whose mothers have the condition can be born premature or at low birth weight, and it can prove fatal in extreme cases.
The experts examined more than two million births between 1967 to 2006 for the study.
Writing online in the British Medical Journal (BMJ), they concluded: "The risk of hyperemesis in a pregnant woman is threefold if the woman's mother had ever experienced hyperemesis in a pregnancy.
"This was regardless of whether hyperemesis had occurred in the pregnancy leading to the woman under study or in a previous or subsequent pregnancy."
Acting as a comparison group, the female partners of men whose mothers had also suffered from the sickness had no increased risk in their pregnancies.
The condition had previously been thought to be caused by psychological factors "such as an unconscious rejection of the child or partner", the experts wrote.
But although psychological factors can play a part - and can worsen as a woman becomes distressed at the level of sickness - this is not the whole story, they said.
Genetics may play a role in the condition alongside environmental factors shared by mothers and daughters, such as same diet, infection or lifestyle.
Copyright © Press Association 2010
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British Medical Journal
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