Why Most Pregnant People Experience Morning Sickness—and How It Could Be Treated

A hormone produced by the fetus may induce nausea and vomiting during pregnancy, a new study finds

Young pregnant woman covers her mouth while standing in front of a table of food
Around 80 percent of pregnant people experience morning sickness, or bouts of nausea and vomiting during pregnancy. skynesher via Getty Images

The nausea and vomiting of “morning sickness” is a familiar sensation to most anyone who has been pregnant: 80 percent of pregnant people experience morning sickness in some form, and around 2 percent endure the more severe hyperemesis gravidarum. This kind of morning sickness comes with so much vomiting that people lose more than 5 percent of their pre-pregnancy weight, and in extreme cases, it can result in hospitalization.

Now, scientists have pinpointed a potential cause of morning sickness. During pregnancy, the fetus produces a hormone known to be responsible for nausea and vomiting, according to a new study published Wednesday in the journal Nature. This knowledge suggests a possible treatment: Changing people’s levels of this hormone before or during pregnancy may stave off morning sickness.

“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 who did not contribute to the findings, tells Nature News’ Carissa Wong.

People typically get morning sickness during the first three months of pregnancy, though it can also last throughout gestation (and despite its name, the nausea isn’t isolated to early hours of the day). While somewhat effective treatments are available, many people do not get adequate care, in part due to fears over medicating while pregnant, writes the Guardian’s Hannah Devlin.

Past scientific research suggested a hormone called GDF15 plays a role in morning sickness. GDF15 is known to be linked to nausea, and it has been tested as a weight loss aid, according to Science’s Catherine Offord. The body can produce a lot of it in response to stress.

The new study is the first to confirm that general morning sickness and hyperemesis gravidarum are tied to higher GDF15 levels. And it’s the first to find elevated levels of this hormone during pregnancy come from the fetal part of the placenta.

“It’s the baby who is making you sick,” study co-author Stephen O’Rahilly, an endocrinologist at the University of Cambridge in England, tells the Wall Street Journal’s Dominique Mosbergen.

Next, the researchers examined genetic data from more than 18,000 people in the Generation Scotland Study. They found that those who had low levels of GDF15 before pregnancy had a higher risk of developing hyperemesis gravidarum during gestation. On the other hand, people with a condition tied to chronically high levels of GDF15 reported very low levels of morning sickness when pregnant.

This finding suggests an individual’s level of GDF15 before pregnancy influences their sensitivity to the hormone produced by the fetus, O’Rahilly tells Nature News.

To test whether giving people GDF15 before pregnancy could prevent morning sickness, the researchers injected mice with it. Mice that received one big dose of the hormone avoided food, while mice that were primed with a slow-releasing dose of GDF15 before the large injection did not seem to lose their appetites, per Science.

The results point to the possibility that priming people with GDF15 before pregnancy could desensitize them from developing morning sickness, though such an injection would need to first undergo human trials.

Another potential treatment could involve blocking GDF15 from binding to its receptor in the brain, per a statement from the University of Southern California.

“We don’t know anything about the role of GDF15 in normal pregnancy,” so future studies will need to test whether affecting its activity has harmful side effects, Catherine Williamson, a clinical researcher in maternal medicine at Imperial College London who was not involved in the research, tells Nature News.

But the findings are inching the field closer to a treatment for severe morning sickness. The study is “a really clever, exciting way to move the research field forward,” Karen Forbes, a reproductive endocrinologist at the University of Leeds in England who was not involved in the study, tells Science. It “could have real clinical implications” for people at risk of hyperemesis gravidarum.

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