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Scientists have identified the hormone that causes morning sickness in pregnant women.

The mystery behind morning sickness - characterised as nausea and vomiting in the first trimester of pregnancy - has been solved by scientists who have recently discovered the specific hormone after studying severe cases of the bodily reaction.

A recently published study in the Nature scientific journal said that the culprit was the hormone GDF15. The University of Cambridge said the hormone is produced by the placenta as well as other tissues outside of pregnancy. In another study from the National Institute of Health, the hormone was linked to causing nausea and vomiting, scientifically referred to as emesis.

Despite being referred to as morning sickness, nausea and vomiting can happen at any time, but according to the Mayo Clinic, it can also develop into hyperemesis gravidarum. Some symptoms of this severe form of morning sickness can result in weight loss and dehydration. The condition reportedly affects up to three per cent of pregnant people and can cause a pregnancy to be classified as “high-risk”.

Dr Marlena Fejzo - a geneticist at the University of Southern California Keck School of Medicine and a co-author of the new study - explained to The New York Times that severe cases of morning sickness aren’t taken seriously in the medical field. She said: “I’ve been working on this for 20 years and yet there are still reports of women dying from this and women being mistreated.”

She added to the outlet that she was interested in finding out what causes hyperemesis gravidarum because of her experience with morning sickness. At the time, the nausea and vomiting were so severe, she had a miscarriage.

Dr Fejzo and fellow scientists at the University of Cambridge checked for the hormone in the blood of pregnant women and identified whether or not the women had genetic risk factors for hyperemesis. Through their research, they found that those experiencing hyperemesis had significantly higher GDF15 levels during pregnancy as opposed to those without symptoms, confirming that the hormone can be a cause of hyperemesis.

However, researchers also found that the hormone’s presence can affect pregnant women differently, as seen in a group of women in Sri Lanka with a rare blood disorder that caused chronically high levels of the hormone. Despite the overwhelming amounts of GDF15, the women rarely experienced morning sickness.

On the results in the Sri Lankan women, Dr Stephen O’Rahilly - a University of Cambridge endricronologist who led the research - confirmed: “It completely obliterated all the nausea. They pretty much have next to zero symptoms in their pregnancies.”

Dr O’Rahilly theorised that a large amount of the hormone in their blood had a protective effect from hyperemesis, and they proceeded to test his hypothesis on mice, giving them small amounts of the hormone. When they reportedly gave the mice a small amount of the dose in the beginning, their appetites were adversely affected. However, after they gave them a larger dose of the hormone three days later, they noted that the mice were more desensitised to its effects.

The scientists said that they hope their research can lead to creating medication that treats hyperemesis that is also safe for pregnant women to take. Thus far, that kind of medication is primarily prescribed to cancer patients.

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