Somewhere between 70 to 80 percent of pregnant people experience nausea and vomiting during pregnancy, aka morning sickness, according to studies. That’s the majority of pregnancies, and yet there is no hard and fast cure for this often debilitating issue. In fact, doctors don’t even know for sure what causes morning sickness, making it hard to prescribe reliable treatments. But a new study may have pinpointed the cause, and — in even better news — might show the way towards better treatments.
The study, published yesterday in Nature, found that the cause of morning sickness is GDF15, a hormone that, when produced by the fetus, triggers vomiting and feelings of nausea. The intensity of the sickness, researchers found, depends on how much hormone is produced and whether the mother has been exposed to it before getting pregnant.
The researchers analyzed data from multiple studies, measuring the amount of GDF15 in pregnant people’s blood while looking at their genetic risk factors for hyperemesis gravidarum, an extreme form of pregnancy sickness that causes relentless nausea, vomiting, weight loss, and dehydration.
One important thing to note: tissues in your body produce low levels GDF15 all the time, including outside of pregnancy. If the pregnant person normally has low levels of GDF15 in their blood, they’ll be more sensitive to it during pregnancy, increasing their risk of experiencing severe morning sickness. For example, the researchers found that a rare genetic variant, known to increase risk of hyperemesis gravidarum, was also associated with lower levels of GDF15 outside of pregnancy. On the other hand, women with the genetic blood disorder beta thalassemia have naturally high levels of GDF15. They typically experience little to no morning sickness.
It all comes down to that one hormone — how much of it the pregnant person was exposed to before pregnancy, and how much is released during pregnancy.
“The baby growing in the womb is producing a hormone at levels the mother is not used to,” Professor Sir Stephen O’Rahilly, leader of the collaboritive study and Co-Director of the Wellcome-Medical Research Council Institute of Metabolic Science at the University of Cambridge, said in a press release. “The more sensitive she is to this hormone, the sicker she will become.”
Crucially, he added, “Knowing this gives us a clue as to how we might prevent this from happening.”
One of the studies the researchers analyzed found that mice given high levels of GDF15 showed loss of appetite, considered a sign of nausea. However, the effect disappeared when the mice were treated with a long-acting form of GDF15 beforehand. That, they think, shows a path towards treating morning sickness in humans as well — by building up a tolerance for the hormone or, O’Rahilly says, by “preventing GDF15 from accessing its highly specific receptor in the mother’s brain.”
The researchers especially hope the findings will be helpful for people with hyperemesis gravidarum. “When I was pregnant, I became so ill that I could barely move without being sick,” said co-author Dr. Marlena Fejzo from the Department of Population and Public Health Sciences at USC, in the press release. Fejzo experienced hyperemesis gravidarum during her own pregnancy. Understanding the cause of the condition, she explained, brings doctors “a step closer to developing effective treatments to stop other mothers going through what I and many other women have experienced.”
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