UCLA researchers have identified a connection between morning sickness symptoms in pregnancy and the body’s inflammatory response to changes that occur during this period. The study, led by anthropologists and epidemiologists at UCLA, analyzed blood samples from 58 Latina women in Southern California during early pregnancy through postpartum to measure immune system molecules called cytokines.
According to the National Institutes of Health, up to 80 percent of pregnant women experience nausea, vomiting, or aversions to certain foods and smells in early pregnancy. These symptoms are generally not considered harmful but rather an indication of the body’s normal adaptation during pregnancy.
“During pregnancy, a mother’s immune system faces a tricky challenge: it has to protect both her and the fetus from infection, but without accidentally attacking the fetus, whose genetic identity is half-foreign because it is half derived from the father. Normally, the immune system attacks anything that seems foreign, so in pregnancy, it has to carefully adjust to keep the fetus safe while still defending against infection,” said UCLA anthropology professor Molly Fox.
Fox is also the corresponding author of “Of scents and cytokines: How olfactory and food aversions relate to nausea and immunomodulation in early pregnancy,” published in Evolution, Medicine and Public Health.
The research team found that 64 percent of participants experienced odor or food aversions—mainly toward tobacco smoke and meat—while 67 percent reported nausea and 66 percent experienced vomiting. The analysis showed that those with aversions to tobacco smoke had a more pronounced inflammatory response. Food aversions, nausea, and vomiting were also linked with a 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 Daniel Fessler.
Researchers suggest these symptoms may be part of an evolutionary process designed to help mothers avoid potentially harmful substances when their fetuses are most vulnerable. However, they caution that further research is needed before drawing definitive conclusions about these mechanisms.
“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,” said Fox.
“Nowadays, you will see labels on packages of ground beef or soft cheese that warn pregnant women to be cautious about these products because of the risks of foodborne illness during pregnancy. Aversions to certain odors and foods, and nausea and even vomiting, appear to be evolution’s way of achieving that same objective,” said Fessler.
The study’s authors believe their findings could help reduce stigma around morning sickness by showing its biological basis as part of healthy pregnancies. They note this understanding could inform workplace accommodations for pregnant employees by supporting more effective health care benefits deployment aimed at reducing absences due to these common symptoms.
Funding for this research was provided by the National Institutes of Health.
