UCLA researchers have identified a connection between symptoms commonly known as “morning sickness” and the body’s inflammatory response during pregnancy. The study, led by anthropology professor Molly Fox, explored how the immune system adapts to protect both the mother and fetus.
“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 Fox.
The research team analyzed blood samples for cytokines—proteins that regulate inflammation—and collected questionnaire data about nausea, vomiting, and aversions to foods or smells among 58 Latina women in Southern California. The study followed participants from early pregnancy through postpartum. Results showed that 64% of participants experienced odor or food aversions (mainly tobacco smoke and meat), 67% reported nausea, and 66% experienced vomiting.
According to Daniel Fessler, UCLA anthropology professor and co-author of the paper: “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.”
Researchers observed that women who avoided tobacco smoke displayed more pro-inflammatory immune responses. Similarly, other symptoms such as food aversion, nausea, and vomiting were linked with this type of immune activity.
Fox explained some unique aspects of human pregnancy: “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.”
Fessler added perspective on evolutionary significance: “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.”
The study’s authors note their findings may support workplace policies aimed at accommodating pregnant employees experiencing these symptoms by providing resources that could reduce stigma and productivity loss.
Funding for this research was provided by the National Institutes of Health.
