Scientists have uncovered why many women experience morning sickness during pregnancy, raising the prospects of a cure for the condition.
The study revealed that a hormone produced by the foetus is the trigger for nausea and vomiting in pregnancy, which in extreme cases can require hospital treatment. Crucially, women who have naturally low levels of the hormone prior to pregnancy tend to be more sensitive to the surge of the hormone, called GDF15, in the first trimester, the research suggests.
“We now know that women get sick during pregnancy when they are exposed to higher levels of the hormone GDF15 than they are used to,” said Marlena Fejzo, a clinical assistant professor of population and public health sciences at the University of Southern California’s Keck School of Medicine, who is the paper’s first author.
Nausea and vomiting affect about 80% of women at some point during pregnancy. About 2% of women, including Catherine, the Princess of Wales, experience an extreme form of morning sickness called hyperemesis gravidarum (HG), which can lead to weight loss, dehydration and hospitalisation. Until now, however, the underlying cause of pregnancy sickness had been unclear.
Although there are some partially effective therapies for pregnancy sickness, the lack of scientific understanding of the disorder, compounded by a fear of using medication in pregnancy, mean that many women are inadequately treated.
Charlotte Howden, the chief executive of the charity Pregnancy Sickness Support, said her GP suggested trying ginger or “eating a little and often” when she sought help for HG, and she was subsequently hospitalised several times during her pregnancy.
“It’s just what we’ve been told to expect in early pregnancy,” she said. “When you are suffering from a condition and no one can tell you why, you start to think: 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.”
The latest research provides multiple lines of evidence linking these symptoms to GDF15. This suggests that lowering the hormone, or blocking its action, could prevent sickness. Another approach could be “priming” women by exposing them to the hormone before pregnancy.
“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,” said Prof Sir Stephen O’Rahilly, a co-director of the Wellcome-Medical Research Council Institute of Metabolic Science at the University of Cambridge, who led the international collaboration behind the discovery.
“We now know why: the baby growing in the womb is producing a hormone at levels the mother is not used to. The more sensitive she is to this hormone, the sicker she will become. Knowing this gives us a clue as to how we might prevent this from happening.”
GDF15 is made at low levels in all tissues outside pregnancy. However, women with a rare mutation in the gene that codes for GDF15 have unusually low levels of the hormone outside pregnancy.
The study, published in Nature, shows that these women are at greater risk of HG during pregnancy, when they are suddenly exposed to high levels of GDF15. But if their foetus also carries the mutation, they are less likely to experience severe symptoms.
Similarly, patients with beta thalassemia, an inherited blood disorder that causes chronically high levels of GDF15, are largely protected against pregnancy sickness.
The research team also showed in mice that exposing mothers to low levels of GDF15 before pregnancy could help prevent pregnancy sickness.
The next step is to test whether priming women who have a history of HG with GDF15 before pregnancy can reduce nausea and vomiting or even prevent the symptoms.