The nausea in pregnancy would have the dual purpose of protecting the fetus from rejection reactions and defending it, together with the mother, from toxic substances.
The morning nausea in pregnancy could be a specific biological mechanism perfected during the evolution to protect the fetus. Research by the University of California in Los Angeles has reconstructed the connections between the complex immune responses triggered by pregnancy, nausea and aversion to certain foods in pregnant women. It is concluded that symptoms of this type in the first months of gestation are, although unpleasant, perfectly normal.
In close contact
Scientists hypothesize that nausea in pregnancy can be part of an adaptive mechanism selected during the evolution that helps the mother’s body to minimize the risks of exposing itself, and exposing the fetus, to harmful substances. In many mammals there are in fact barriers that separate the fetus from the maternal blood, in which immune cells circulate. In man it is not so: maternal blood enters the placenta to nourish the fetus and provide it oxygen, and therefore strategies are needed to prevent the mother’s immune system from unleashing against the unborn child, which has a “foreign” DNA.
Game of balance
“As a rule, the immune system attacks whatever it seems extraneous, therefore, in pregnancy, it must adapt carefully to keep the fetus healthy while continuing to defend itself from infections”, explains Molly Fox, anthropologist of the Californian university that coordinated the study.
To reach this delicate balance, the mother’s body puts a peculiar chain of inflammatory responses in a way; These immunological changes in turn can induce nausea, an answer that encourages the avoidance of certain potentially dangerous foods and that guarantees a further protection layer.
The nausea during pregnancy would have the same purpose as the labels that warn women pregnant on the risks of certain fresh cheeses or raw meats: it has, like these, the goal of discouraging the consumption of food that could cause dangerous infections.
The role of inflammation
Together with colleagues epidemiologists, scientists analyzed the levels of cytokines (immune molecules that send alarm signals and regulate the inflammatory mechanisms in case of infection) in the blood of 58 pregnant women, from the first weeks of pregnancy to after childbirth. The participants also completed questionnaires about the entity of nausea in pregnancy and aversions to certain foods found at that time.
64% of the interviewees had experienced some aversion to smells and foods (for example towards cigarette smoking, or meat). 67% said they had suffered from nausea and 66% had vomited. The analyzes found a relationship between the presence of cytokines that promote inflammation and aversion to certain types of foods, nausea and vomiting.
The test of a connection between the immune responses and the mechanisms that trigger morning nausea.
Concrete repercussions
The authors of the study hope that normalizing nausea in pregnancy and understanding it with a view to its biological function can contribute to a better understanding of this disorder at the level of society: for example, which reduces prejudices towards women who must be absent for this reason from the workplace.
