Of scents and cytokines: How olfactory and food aversions relate to nausea and immunomodulation in early pregnancy.

Background: During pregnancy, the maternal body undergoes extensive physiological adaptations to support embryonic growth, including whole-body remodeling, that may induce odor and food aversions, as well as nausea and vomiting. The biological mechanisms behind odor and food aversions, as well as nausea and vomiting in early pregnancy, remain largely unexplored. Our study investigated associations between these changes and cytokine profiles during pregnancy.

Methodology: A cohort of pregnant Latina women in Southern California (n = 58) completed a structured questionnaire on pregnancy "morning sickness"-related symptoms and aversions. Maternal plasma cytokine levels were measured between 5 and 17 weeks' gestation.

Results: About 64% of participants experienced odor or food aversions, primarily to tobacco smoke and meat; 67% reported nausea, and 66% experienced vomiting. Multivariable linear regression models revealed that odor aversions were associated with increased pro-inflammatory T-helper-cell type (Th) 1 composite cytokine levels. Women who found tobacco smoke aversive exhibited a shift toward Th1 immune responses, indicated by a higher Th1:Th2 ratio. Food aversions also showed a positive association with Th1 cytokine levels. A borderline positive association was noted between nausea and vomiting and the Th1:Th2 ratio.

Conclusions: These findings are consistent with the hypothesis that gestational changes in olfactory and gustatory experience, and nausea and vomiting, reflect adaptive upregulation of behavioral prophylaxis in ways that could protect the fetus. If this elevated Th1:Th2 ratio and pro-inflammatory phenotype are part of the maternal and embryonic response to embryogenesis, the behavioral and biological markers that we explore may provide an accessible index of fetal development during early pregnancy.