Scientists have uncovered why women experience intense nausea and vomiting during pregnancy.

The study, published in the journal Nature, found that a single hormone is responsible for pregnancy sickness.

The hormone, GDF15, is produced by the fetus and triggers nausea and vomiting in the mother by activating neurons in the mother's brain stem. The study also found that the severity of pregnancy sickness is linked to the amount of the hormone in the mother's blood before and during pregnancy.

Researchers hope the discovery will lead to better treatment of the debilitating condition, as well as of more severe forms of pregnancy sickness like hyperemesis gravidarum, which can be life-threatening.

Pregnancy sickness can be life-threatening

"The idea of morning sickness — merely feeling sick during the morning — perpetuates in the media, but this isn't the reality. Many women experience consistent and unrelenting nausea and vomiting which can go on for the entire pregnancy," said Charlotte Howden, CEO of the UK-based charity Pregnancy Sickness Support.

Between 70-80% of all pregnant women suffer from some form of pregnancy sickness, but symptoms are on a spectrum and range from mild to severe.

Howden told DW she suffered from vomiting up to 30 times per day during her pregnancy. "It was very serious. You become a shadow of your former self. You can't work or look after other children. It's a huge issue for the family unit."

Between 1-3% of women experience hyperemesis gravidarum, a severe form of pregnancy sickness that often needs hospital treatment.

"It's widely reported as a rare condition, but if you look at the statistics, 3% is a lot of people — in the UK that's around 30,000 women per year," said Howden.

The condition can be life-threatening for mother and child, owing to the mother's inability to keep nutrients and fluids down.

"Severe hyperemesis is the commonest cause of admission to hospital in the first trimester of pregnancy. Today there are women who are driven to terminate their very much wanted pregnancy because of the severity and under-treatment of their hyperemesis symptoms," said Roger Gadsby, a specialist in pregnancy sickness at the University of Warwick in the UK.

New hope for hyperemesis treatments

The study found that the women experiencing hyperemesis had higher levels of GDF15 in their bloodstream during pregnancy than women who had no symptoms.

The severity of pregnancy sickness also depends, however, on the level of GDF15-signaling before pregnancy. The study found that women with naturally low levels of GDF15 before pregnancy are more sensitive to increases of GDF15 during the first trimester.

"The article opens up the possibility of treating hyperemesis. One possibility would be to raise GDF15 levels in women with low levels before pregnancy. Another would be to look at the possibility of safely reducing GDF15 levels in women suffering from hyperemesis," said Gadsby. 

Hyperemesis 'underdiagnosed and undertreated'

Howden hopes the study will draw more attention to women's health during pregnancy. She said many women with severe forms of pregnancy sickness are often dismissed as having normal morning sickness.

"Hyperemesis is hugely underdiagnosed and undertreated. People don't often realize how complex and severe pregnancy sickness can be," said Howden.

"We know a lot about menstruation and menopause, including about treatments. Now we know more about pregnancy sickness and hyperemesis, it gives hope. Obviously this won't happen overnight, but the hope is that the next generation of sufferers will have treatment available, which would be incredible," she added.

Edited by: Lucy James