Study uncovers protective function of morning sickness

Morning sickness symptoms such as nausea and food aversions are linked to healthy inflammatory responses that help protect both mother and fetus during pregnancy, new research shows.

Up to 80 per cent of early-stage pregnant women experience nausea, vomiting and aversions to certain foods or smells.

Researchers say these symptoms point to a delicate immune balance rather than health problems.

The responses appear to be part of the body’s mechanism for tolerating the half-foreign fetus while avoiding potentially harmful substances.

UCLA researchers studied blood samples from 58 Latina women in Southern California, measuring cytokines — proteins that regulate immune responses — while tracking morning sickness symptoms through questionnaires.

Sixty-four per cent reported odour or food aversions, mainly to tobacco smoke and meat. Sixty-seven per cent experienced nausea and 66 per cent vomiting.

Women with aversions to tobacco smoke showed a stronger shift toward inflammatory responses. Nausea, vomiting and food aversions were also tied to more pro-inflammatory immune activity.

Molly Fox, UCLA anthropology professor and corresponding author, explained the challenge for the immune system in pregnancy.

She said: “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.”

The researchers believe this immune balance protects mother and fetus while behavioural responses — such as avoiding certain foods — add another safeguard, especially in the first and second trimesters.

Daniel Fessler, UCLA anthropology professor and co-author, stressed the protective role of these symptoms.

He said: “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.”

Fox noted that human pregnancies face unique challenges.

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 that these responses may be evolutionary adaptations.

The researcher said: “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 odours and foods, and nausea and even vomiting, appear to be evolution’s way of achieving that same objective.”

The team said their findings could help reinforce the idea that nausea and vomiting are normal pregnancy symptoms with biological roots, potentially supporting calls for workplace adjustments and reducing stigma.