Scientists believe they have figured out the cause of severe morning sickness during pregnancy.

It turns out - some women are more sensitive to a hormone called GDF15, released by a growing fetus while in the womb, Nature first reported, linking a study published on Dec. 13.

Morning sickness is common in pregnancy, especially in the first trimester. Around 70% of women report dealing with it. But hidden in that 70% is a much smaller group of expectant moms (3%) who experience morning sickness drastically different.

Those women are often met with the same advice as all women: to snack often, drink water and watch their activity. But this form of nausea, known as hyperemesis gravidarum, isn't usually escapable.

“For the first time, hyperemesis gravidarum could be addressed at the root cause, rather than merely alleviating its symptoms,” Tito Borner, a physiologist at the University of Pennsylvania, said.

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The finding could mean prevention is possible

“We now have a clear view of what may cause this problem and a route for both treatment and prevention,” study co-author Stephen O’Rahilly, a metabolism researcher at the University of Cambridge, said.

According to the research, women with high levels of the hormone GDF15 before pregnancy, had minimal reactions to it when pregnant. Therefore, giving GDF15 to women at risk of hyperemesis gravidarum before conceiving, could mean protecting them from the condition entirely.

GDF15, produced at low levels by certain organs, can trigger nausea by "binding to specialized receptors in the brainstem," the study states. The hormone increases after ingesting toxic substances during pregnancy, causing sickness. “It’s usually worst in the first trimester and then it gradually fades,” O’Rahilly shared.

O’Rahilly proposed that GDF15 could have evolved "to protect people from poisoning themselves and to shield a developing fetus from toxic substances."

In the latest study, he and other researchers compared GDF15 levels produced by placental cells from both mom and baby and found that fetal cells produced most of the hormone.

The test

After analyzing the genetic data of over 18,000 participants, scientists found higher levels of GDF15 present before pregnancy lessened the risk of severe nausea during pregnancy, confirming that people react very little to the hormone while pregnant if higher levels are present before conceiving.

Researchers tested this by injecting one group of mice with GDF15 and another with a placebo. After three days, all mice were given another injection of GDF15. Those that had received that placebo became ill, eating less and losing weight, but those with the double GDF15 injection, were just fine.

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So, what's next?

Well, we know that those with low levels of GDF15 could be given high doses of the hormone while trying to conceive, which should desensitize them to hyperemesis gravidarum during pregnancy, O’Rahilly said.

And at least two antibodies against GDF15 are being tested in clinical trials that would treat cachexia, a complex problem that is more than a loss of appetite.

Though, further research is needed to explore these possibilities. “We don’t know anything about the role of GDF15 in normal pregnancy,” said obstetric clinician and researcher Catherine Williamson at Imperial College London. Scientists need to figure out if messing with the hormone’s activity will have harmful side effects, Williamson added.

Nonetheless, if GDF15 is a primary driver of severe nausea during pregnancy, and its effect can be managed because the source is now known, that is a major win for the health industry and for women everywhere.