Scientists have finally uncovered why many women experience morning sickness during pregnancy, identifying a hormone produced by the foetus as the trigger. The breakthrough, achieved by an international collaboration led by the University of Cambridge, offers hope for a possible cure for the debilitating condition.
The research, published in Nature, reveals that the hormone GDF15, produced in the foetus, causes nausea and vomiting. Women with naturally low levels of this hormone before pregnancy are particularly sensitive to the surge in the first trimester, leading to more severe symptoms. About 80% of pregnant women experience some nausea, while 2%, including the Princess of Wales, suffer from hyperemesis gravidarum (HG), which can require hospitalisation.
“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 Dr Marlena Fejzo, first author from the University of Southern California. Professor Sir Stephen O’Rahilly, co-director of the Wellcome-MRC Institute of Metabolic Science at Cambridge, added: “Knowing this gives us a clue as to how we might prevent this from happening.”
Evidence from rare genetic mutations supports the finding. Women with a mutation causing exceptionally low GDF15 outside pregnancy face higher HG risk, but if the foetus also carries the mutation, symptoms are milder. Conversely, patients with beta thalassemia, who have chronically high GDF15, are largely protected against pregnancy sickness.
The study suggests two potential approaches: blocking the hormone or its action, or “priming” women by exposing them to low GDF15 before pregnancy to build tolerance. Animal experiments in mice have shown that pre-pregnancy exposure can reduce sickness.
Charlotte Howden, chief executive of Pregnancy Sickness Support, highlighted the lack of understanding until now. “When you are suffering and no one can tell you why, you start to think: is it something I’ve done?” she said. The team plans next to test priming in women with a history of HG, aiming to reduce or prevent symptoms.
