A study recently published in Evolution, Medicine, and Public Health provides new insight into the involvement of the immune system during the first trimester of pregnancy, and how this may influence many pregnancy-related symptoms, such as nausea, vomiting, and food and odor aversions. This study included 58 women living in Southern California (between the ages of 20-42) from Wave 2 of the Mothers’ Cultural Experiences (MCE) study. Women included in the study were less than 17 weeks pregnant at the study’s onset, completed questionnaires about food and odor aversions as well as nausea and vomiting, and had cytokines measured from non-fasting morning samples collected between weeks 5 and 17.
Approximately 64% of women in the study had odor aversions, most commonly to tobacco smoke, and 64% also had aversions to foods, most frequently to meat. Women with more odor aversions had longer-lasting nausea as well as more food aversions.
In a fully adjusted model, odor aversion was associated with the Th1 composite cytokine level, suggesting that a more inflammatory immune balance was linked to greater aversions. Similarly, a greater Th1:Th2 composite ratio was associated with more nausea and vomiting, reflective of an interaction between a more inflammatory immune state and nausea, vomiting, and food/odor aversions.
The specific mechanisms involved are still incompletely understood, as is the sequence of events. For example, does an inflammatory immune response trigger aversions and nausea, or could the reverse be true? It does remain consistent with the hypothesis that mild-moderate nausea (but not severe) may be an evolutionarily adaptive mechanism, protecting fetal development, combined with a more inflammatory immune response, which provides protection from infection.