Smell perception during early pregnancy: no evidence of an adaptive mechanism

Objective It has been suggested that nausea and vomiting in pregnancy is an evolutionary adaptive mechanism to avoid the ingestion of potentially harmful foods. It has also been suggested that the mechanism that triggers nausea and vomiting in pregnancy may be olfaction and that olfactory senses are invoked to provide this protection. This study aimed to test this theory in a systematic design. Design Cross sectional study. Setting The antenatal department of a maternity hospital in the north of England. Sample Three groups of participants: pregnant women (n = 55), non- pregnant women ( n = 42) and men ( n = 48). Methods Sensitivity was tested towards the odours of six standard stimuli ( half safe and half associated with potentially harmful compounds). Main outcome measures Odour rating of likeness, strength and pleasantness. Results Pregnant women rated safe and odours with potentially harmful compounds differently but not more so than men or non- pregnant women. There was no evidence that pregnancy changed the olfactory processes from the non- pregnant state and only slight differences between pregnant women and men were recorded. Conclusions There was no evidence that olfactory processes had undergone any adaptation during pregnancy. The ability to differentiate safe from potentially harmful compounds was common to all three groups studied.