What May Be Behind Morning Sickness, According to a New Study

For more than 80% of pregnant women morning sickness can strike at any time in the first trimester. The sudden waves of nausea, strange food aversions and gagging over everyday smells can make those early months especially tough. But a new study suggests there may be a very good reason behind it all.

Researchers at UCLA recently set out to better understand why morning sickness happens. They surveyed 58 pregnant women about their symptoms and tested their blood for immune system molecules called cytokines—some that trigger inflammation (pro-inflammatory) and others that help calm it down (anti-inflammatory)

Of the women in the study, 64% reported experiencing odor or food aversions, primarily to tobacco smoke and meat, while 67% reported nausea and 66% experienced vomiting. When researchers compared blood samples, they found that women with symptoms showed a noticeable shift toward more inflammation. In particular, aversion to tobacco smoke was linked to stronger inflammatory responses. Food aversions, nausea and vomiting were also tied to a more pro-inflammatory immune balance.

“Nausea, vomiting or aversions to foods or smells are not indications that something is going wrong for the mother or the fetus. It’s likely an indication that everything is moving along normally, and a reflection of the body’s healthy and helpful immune response,” said UCLA anthropology professor and paper co-author Daniel Fessler in a press release.

Study co-author and UCLA anthropology professor Molly Fox added that human biology makes this process even more important. “In many mammals, the fetal compartment has barriers separating it from the mother’s blood supply, where her immune cells are. But in humans, we have a unique setup—fetal cells are bathed in maternal blood. Humans have the most invasive of all placentas, burrowing deep into maternal tissue. So humans need unique strategies to prevent the mother’s immune system from attacking the fetus,” Fox said.

According to the researchers, these complex immune changes may trigger nausea, which then leads to food avoidance as an added layer of protection. In other words, that queasy feeling that comes and goes may actually be a direct result of your body fighting hard to protect you and baby.

While the study’s authors note that the evidence is not definitive and more research is needed, their findings lend weight to the fact that not only is morning sickness normal, but it may also serve a vital role in keeping you and baby safe.

Fighting morning sickness? Find relief with these parent-tested and doctor-approved remedies.