A near-debilitating form of morning sickness experienced by some pregnant women may be caused by the woman’s reaction to a hormone the fetus releases in the early stage of pregnancy. The findings offer hope of preventing or treating the extreme nausea, which is called hyperemesis gravidarum.

The study, by researchers at the University of Southern California and the University of Cambridge, was just published in the journal Nature.

About 4 out of 5 pregnant women experience nausea and vomiting during at least some portion of pregnancy. But 2% experience an extreme form called hyperemesis gravidarum, which the researchers note can lead to weight loss, dehydration and hospitalization. In a release on the study, they note that a “growing body of evidence has linked the symptoms to GDF15, a hormone produced in the placenta that increases substantially during pregnancy.”

Those with low levels of the hormone before they are pregnant have the worst symptoms because they are exposed in pregnancy to more of the hormone than they are used to, said Marlena Fejzo, a clinical assistant professor at the Keck School of Medicine and the paper’s first author.

She said that she is among women who have suffered the effects of extreme morning sickness during pregnancy.

Women who are more sensitive to the hormone get the sickest, said Dr. Stephen O’Rahilly, a professor and co-director of the Wellcome-Medical Research Council Institute of Metabolic Science at the University of Cambridge, who led the collaboration. “Knowing this gives us a clue as to how we might prevent this from happening.”

The researchers believe that the hormone could potentially be reduced during pregnancy, noting their study suggests that is likely a safe option. Another option might be “priming” the women for the higher levels of the hormone by exposing them to it before pregnancy.

“This study provides strong evidence that one or both of those methods will be effective in preventing or treating” the morning sickness, Fejzo said.

About the study

The researchers used patient genetic analyses and blood tests, as well as studies of human cells and mice to look at how the hormone is related to extreme morning sickness. Among other things, they found a rare genetic mutation in the gene that leads to an unusually small amount of the GDF15 hormone throughout the body, creating the risk that they’ll react when exposed to high amounts of it from the fetus.

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If the baby inherits the mutation and produces abnormally low levels, the researchers think the mother will be less likely to develop hyperemesis gravidarum. Women with an inherited blood disorder called beta thalassemia, which leads to high levels of the hormone, don’t usually experience much morning sickness.

When mice were exposed to the hormone before pregnancy, they didn’t have the same appetite loss that indicates the rodent version of morning sickness, the researchers found.

The team also looked at what happens when a mother and her developing baby both have low levels of the hormone. “Babies were born normal and healthy,” they reported.

Fejzo has applied for funding to test whether metformin, a drug that raises that particular hormone level, is safe for use by patients who have already experienced hyperemesis gravidarum during pregnancy. They also want to test a different class of drugs to see if it reduces the extreme nausea.

According to an article on the study on nature.com, “Further research is needed to explore these possibilities. ‘We don’t know anything about the role of GDF15 in normal pregnancy,’ says obstetric clinician and researcher Catherine Williamson at Imperial College London. Studies should establish whether changing the hormone’s activity might have harmful side effects, she says.”