Scientists think they have finally pinpointed the cause of morning sickness – and could one day find a treatment for the most severe cases.
Recent studies have suggested morning sickness is caused by the hormone GDF15, produced by both men and women but seemingly elevated during pregnancy.
However, researchers were unsure whether it was GDF15 produced by the mother of the baby causing morning sickness, which in severe cases is known as hyperemesis gravidarum (HG), sometimes resulting in hospitalisation.
In 2012, Catherine, the Princess of Wales, then the Duchess of Cambridge, was hospitalised with the condition while pregnant with Prince George.
To better understand the condition, the team analysed data from women recruited to various studies, including at the Rosie Maternity Hospital in Cambridge.
They found the level of nausea experienced by women in pregnancy related to the amount of GDF15 produced by the foetal part of the placenta.
The level of sickness also rested on how much of the hormone the woman had been exposed to prior to pregnancy.
Professor Sir Stephen O’Rahilly, director of the Medical Research Council metabolic diseases unit at the University of Cambridge, said: ‘Most women who become pregnant will experience nausea and sickness at some point, and while this is not pleasant, for some women it can be much worse – they’ll become so sick they require treatment and even hospitalisation.
‘We now know why – the baby growing in the womb is producing a hormone at levels the mother is not used to.’
GDF15 is made at low concentration in most of the body’s organs. A woman with lower levels in her blood outside of pregnancy may be at a higher risk of developing severe morning sickness in pregnancy, known as HG, researchers said.
HG can lead to prolonged periods of vomiting, dehydration and weight loss. Treatments include anti-sickness medicines and steroids, but some women may require hospitalisation and intravenous fluids.
‘The more sensitive she is to this hormone, the sicker she will become,’ added Sir Stephen. ‘Knowing this gives us a clue as to how we might prevent this from happening.
‘It also makes us more confident that preventing GDF15 from accessing its highly specific receptor in the mother’s brain will form the basis for an effective and safe way of treating this disorder.’
Studies in mice suggested that building up a tolerance prior to getting pregnant could prevent sickness, offering hope for a new treatment.
Researchers also said women with the inherited blood disorder thalassemia, which causes higher levels of GDF15 outside of pregnancy, experienced little to no nausea or vomiting when pregnant.
Charlotte Howden is chief executive of Pregnancy Sickness Support and was hospitalised with HG after vomiting up to 30 times a day.
She visited her GP but was told there was nothing they could do. After having tests, she was given medicine that left her ‘comatose’ and was eventually admitted to hospital.
How long does morning sickness last?
Usually, morning sickness symptoms start from the six week mark – around two weeks after a woman misses her period.
However, some women can feel nauseous around two to three weeks in.
For many, it’s the first sign that they might be pregnant.
Morning sickness is usually over by the end of the first trimester, with appetite returning to normal at the 12-15 week mark.
However, this isn’t a general rule, and sickness can sometimes continue into the second trimester.
Some women will feel sick throughout their pregnancy, and some will feel extreme morning sickness.
This happened three times, with Ms Howden describing ‘a complete disconnect between my GP and the consultant’.
She was eventually put on the right treatment at week 16 of her pregnancy.
Ms Howden, who gave birth to son Henry in 2016, added: ‘When you are suffering from a condition and no-one can tell you why, you start to think, oh, is it me? Is it something I’ve done?
‘I’m so grateful for the dedication of the researchers, because this isn’t a condition that really ever made the headlines until the now Princess of Wales suffered with it. It wasn’t an area of research that people were really interested in. It was just morning sickness – why should we care?”
UK funders of the study were the Medical Research Council and Wellcome, with support from the National Institute for Health and Care Research Cambridge Biomedical Research Centre.
The study is published in the journal Nature.
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