Researchers Say They Now Know What Causes Morning Sickness

If you've been pregnant, chances are you've experienced nausea and vomiting.

Fact checked by Sarah Scott

There are few things more synonymous with pregnancy than morning sickness (despite it not always happening in the morning). It’s often one of the first hints that someone is pregnant or the butt of a pregnancy joke, and that’s because an estimated eight out of ten pregnant people experience it.

“[Nausea and vomiting] can negatively affect the health and quality of life of a pregnant person,” says Libby Wetterer, MD, a family physician with Penn Medicine. “Unless severe, it generally does not affect the health of the infant.”

For many birth givers, nausea and vomiting during pregnancy isn’t just a minor annoyance, it can be debilitating, and there's not much that can be done to alleviate the symptoms. That’s why researchers from Cambridge University and the Keck School of Medicine at USC sought to understand the causes of morning sickness in hopes of one day preventing and better treating it.

“We've been interested in this hormone called GDF15 for several years now,” says Sam Lockhart one of the authors of a new study about the hormone which they found impacts the severity of pregnancy nausea. “It's been around for decades, but wasn't really until 2017 that four different pharmaceutical companies worked out what it likely does.”

What Does the GDF15 Hormone Have To Do With Morning Sickness?

The Cambridge University study team built upon previous research on GDF15 which showed that the hormone acts on a very small part at the base of the brain and essentially signals nausea and distress which makes people vomit.

“If you imagine that normal levels of GDF15 are around 500 to 800 grams per mil, in healthy people when you get pregnant, they go up to about 10 or 20,000 [grams per mil],” Lockhart says.

Understanding GDF15’s effect on the brain coupled with the fact that it’s produced entirely by the fetus in the placenta allowed researchers to really put together what was happening when pregnant people experience morning sickness.

How Researchers Studied GDF15

Researchers working on the study used a multidisciplinary approach to studying GDF15 in pregnant people. They utilized different types of prior studies and pieces of evidence which all came together to give them a better look at what was going on with GDF15.

One of the first things they did was look at levels of GDF15 in the blood of women with and without a condition called hyperemesis gravidarum which is severe pregnancy sickness.

“What we found was that women who had hyperemesis gravidarum versus women who attended hospital at similar times in their pregnancy, but for other reasons, their levels of GDF15 were higher,” Lockhart explains. “But what struck us was even though there was this difference, there's a big overlap of the two populations, so it wasn't like they were very, very far apart, they're kind of overlapping, which suggests there was something more complicated going on.”

The next thing the researchers did was look at pregnant people who were at very high risk of developing hyperemesis gravidarum due to mutations in their DNA either in or around the GDF15 hormone.

“And what we found, surprisingly, was that women who had these mutations actually had lower levels of the sickness hormone when they're not pregnant. So in the non-pregnant state, they have lower levels of the hormone. So that was a bit of a paradox, right?” Lockhart says.

This was an interesting finding for the team. Basically, the pregnant people who already had high levels of GDF15 in their bodies before they were pregnant had a sort of tolerance to the impact of the increased hormone levels during pregnancy, which means nausea and vomiting didn’t affect them as intensely. But to be sure their findings held up, the researchers tested the theory with mice.

“If the mice had chronically high levels of GDF15, they were resistant to the high GDF15 dose. If they had chronically low levels, then they were particularly sensitive to it,” Lockhart explains. “The overall model is that it is the GDF15 coming from the baby in pregnancy that’s making you sick. But one of the key determinants is how sensitive you are to that hormone in your blood. And what determines that sensitivity is in part how much your own body makes before you become pregnant.”

What This Means For Pregnant People 

Lockhart and his team’s findings help us understand morning sickness in a different way. The findings show that how intense a person’s nausea and vomiting during pregnancy is largely dependent on the makeup of their DNA. But there are some other factors that impact the severity of sickness.

“If you've got twins, [GDF15] is higher in that pregnancy,” Lockhart says. “And also if the baby is female, that puts GDF15 up as well in pregnancy, and it also makes you more likely to have morning sickness, actually.”

On the other hand, if you’ve been pregnant before, and already exposed to high levels of GDF15, then your likelihood of developing bad nausea and vomiting is decreased, Lockhart adds. The research team also plans to build on their findings to find actual genetic risk factors.

“One of the implications of your baby making all this [GDF15] is that it's not the mom's DNA or the mom's genome that is determining how much of this has been in pregnancy, it's all the baby's genome that’s determining it,” Lockhart says. “So what we have some evidence of is that if you carry a mutation, that makes you more likely to have severe morning sickness. But if your baby carries that as well, it also protects you. So you're slightly less likely to get it if your baby doesn't have it. What we're doing is trying to study that in more detail.”

The researchers hope to use their future findings to help develop better, more targeted treatment for morning sickness, which is a much-needed advancement for maternal health. As Dr. Wetterer explains, because morning sickness is so common, it’s prone to minimization.

“Friends, family, healthcare providers, and sometimes even patients themselves may minimize symptoms,” says Dr. Wetterer. “It's important to bring up with a trusted prenatal provider because symptoms are easier to treat the earlier you start.”

For Lockhart and his team, the minimization of such a debilitating illness is part of what drives them to continue working to not only understand it more but to offer better assistance to those experiencing it.

“Unfortunately, this condition is subject to a lot of stigma,” Lockhart says. “I think that's partly because it's so poorly understood. I hope that also providing some biological detail about what's going on, will help remove that stigma, and convince people that it is a real meaningful thing, that variation and survivability aren't psychosomatic or in someone's head, it's biology, you can't find your biology, unfortunately. So that's kind of one concrete thing I think we can offer already.”

For more Parents news, make sure to sign up for our newsletter!

Read the original article on Parents.