Scientists may have found the cause of morning sickness - and hope for treatment

Pregnant woman
Scientists have searched for years to understand the cause of morning sickness and hope that they may one day find a cure for it. Photo credit: Getty Images

By Jen Christensen of CNN

Most people who get pregnant develop a condition called morning sickness; some, like Catherine, Princess of Wales, and actress Amy Schumer, have such severe forms that they need to be hospitalized, and some women even die from it.

Scientists have searched for years to understand the cause in the hopes that they may one day find a cure for it.

A study published this week in the journal Nature suggests that some pregnant people are particularly sensitive to a hormone called GDF15. It's produced at low levels throughout the body, but a pregnant person gets another strong dose from the growing fetus, and that can trigger nausea and vomiting. Studies done with cancer patients have found that when the body produces too much GDF15, it can lead to chronic nausea and weight loss. 

2018 study found a link between the gene that controls GDF15 and nausea and vomiting in pregnancy in 53,000 women. The new paper builds on that work and establishes this connection between the hormone and the condition by looking at the issue from a variety of perspectives, including genetic information and data from a new test that can determine what hormones are in a pregnant person's blood and at what level, in addition to studies in mice and in the lab.

The researchers found that levels of GDF15 rise in the first 12 weeks of pregnancy. The higher the levels of the hormone from the foetus and the more sensitive the pregnant person was to the hormone, the sicker she got. When the foetus produces less GDF15, the risk of getting sick seems to be lower. Her exposure to it before pregnancy also can be a factor.

The scientists also looked at research that said people who had a particular inherited blood disorder and who had high levels of the hormone in their body before they became pregnant almost never got sick during pregnancy. They also saw the inverse: Those who have a rare genetic variant that causes them to have low levels of GDF15 are at a much higher risk of hyperemesis gravidarum. The authors also found that when mice were exposed to high levels of GDF15, they lost their appetite, suggesting they were experiencing nausea. When they were treated with a long-acting form of the hormone, they had a regular appetite.

When morning sickness becomes dangerous 

About 70 percent to 80 percent of people who get pregnant get what's commonly called "morning sickness," although pregnant people can feel nauseated and vomit any time of day.

More than 2 percent develop a severe form called hyperemesis gravidarum or HG. It can be dangerous since it leads to dehydration and can cause the pregnant person to lose weight. It also may have negative impacts on the baby, including causing premature birth, neurodevelopmental disorders or even miscarriage.

Study co-author Dr Marlena Fejzo, a geneticist and clinical assistant professor at the University of Southern California Keck School of Medicine, knows these serious effects from experience.

"After I lost a baby from it, I was really motivated to try to figure out what was happening," she said. 

When she started looking into what caused hyperemesis gravidarum, she said, there really wasn't a lot of research, possibly in part due to how dismissive some doctors are when pregnant patients tell them they have morning sickness.

Fejzo says she's heard from women whose doctors are dismissive of the problem and tell them that they'll get over their nausea in a few months. She even heard a professor tell her medical students that someone hospitalized with hyperemesis gravidarum is there because "there's usually something going on at home." Fejzo's own doctor told her the problem "was all in her head." Yet Fejzo, who also works with the HER Foundation, an organization raising awareness about hyperemesis gravidarum, said people who have had the condition with a first pregnancy often reach out to learn if there is a way to avoid it.

People with morning sickness are sometimes told to take anti-nausea medications and advised to get lots of rest, drink plenty of fluids and avoid nausea triggers like smells. But knowing what causes any form of morning sickness, severe or mild, could help scientists find a cure - or at least a better way to relieve symptoms.

Doctors can prescribe anti-vomiting medications and vitamin B1 to women with HG, which can be helpful to protect the pregnant person's heart and brain and to support the baby's development. 

Studies now underway are looking at ways to prevent the hormone-induced stomach upset in cancer patients, but none have involved pregnant people.

It's possible, Fejzo said, that there may be a way to safely expose the person to this hormone before they become pregnant, to build up their tolerance. She's submitted a grant for a trial to investigate what the right dosing may be.

Fejzo said she wakes up every day determined to help people with morning sickness, especially those with HG.

"Many people decide not to have a baby again after having a pregnancy like this," she said. "There's still so much more to do. This is not the end of the story."