Olfactory modulation of nausea during early pregnancy?

To investigate whether nausea and vomiting and olfactory sensitivity are correlated, we determined whether subjects with little or no nausea and vomiting are less sensitive to odours than subjects who indicate a high degree of nausea and vomiting, and whether subjects with relatively low olfactory sensitivity are less prone to nausea and vomiting than subjects with relatively higher olfactory sensitivity.

Cross sectional study.

The Unit of Perinatal Physiology, Department of Obstetrics, University Hospital, Zurich, Switzerland.

Fifty-three women in early pregnancy.

Following a detailed history related to olfaction and nausea and vomiting, subjects filled in a nausea profile which provided a 'general nausea score' comprised of the factors 'somatic distress', 'gastrointestinal distress', and 'emotional distress'. Olfactory function was assessed using pen-like odour dispensing devices ('sniffin' sticks'). Tests included n-butanol odour threshold, odour discrimination and odour identification.

Olfactory function assessed by means of the sniffing sticks nausea profile.

Correlational analyses between results of olfactory sensitivity and scores from the nausea questionnaire were not significant. Further, when subjects were divided into groups with relatively low or relatively high overall scores in the nausea profile, olfactory sensitivity did not differ between groups. Similarly, other analyses did not indicate a modulation of nausea and vomiting through olfactory sensitivity.

These findings do not support the hypothesis that higher olfactory sensitivity relates to an increase of nausea. However, they do support the idea that olfactory-induced nausea is independent of subjectively perceived intensity. Olfactory-induced nausea appears to be due to the cognitive processing of olfactory information which, in early pregnancy, is reported to be altered in an unsystematic fashion.