An empirical study of the maternal-embryo protection hypothesis: Public health implications

The nausea and vomiting of early pregnancy (NVP) affects three-fourths of all pregnancies worldwide. Food aversions, food cravings, and other somatic symptoms are also common during early pregnancy. The maternal-embryo protection hypothesis (MEPH) proposes that early pregnancy nausea and vomiting (NVP), food aversions (FA), and heightened somatosensory sensitivity (HSS) evolved together as a symptom complex to protect pregnant women and their embryos from foods containing abortifacent/teratogenic phytochemicals and pathogenic microorganisms. While this hypothesis is intriguing and has a number of proponents, its support is largely based on circumstantial evidence. The scarcity of empirical data makes it difficult to support or refute this controversial theory and argue for or against clinical advice published by its proponents. The present study tested MEPH predictions in a large prospective cohort (n=849) of Ecuadorian women followed from the first trimester through early postpartum. Repeated data on NVP, FA, HSS, and other symptoms were collected by questionnaire during the first 20 gestation weeks. Miscarriage and congenital anomaly cases were assessed using established criteria. As predicted, women with NVP were more likely to develop HSS and FA, including specific aversions for meats, bitter/pungent vegetables, spicy/hot, and fried/roasted/grilled foods. Different from predictions, food odor, not taste, was identified as the primary aversion trigger for FA and women with NVP were more likely to develop aversions for “low toxicity” starches.  Furthermore, the data did not support a protective role for the hypothesized symptom complex other than that contributed by NVP itself.  If natural selection is operating, the mechanisms involved may be different than what circumstantial evidence suggests. Following advice based on this unsupported theory could result in decreased dietary diversity or symptom under-treatment. Pregnant women should be discouraged from following this advice.