Nausea and vomiting in pregnancy: a review.

Throughout pregnancy, women with nausea and vomiting in early pregnancy showed a different metabolic pattern compared to asymptomatic pregnancies. Women suffering from nausea and vomiting seem to have a low "functional reserve" of their liver capacity and could tentatively be described as hypersensitive to estrogens or their metabolites, e.g., catecholestrogens. These steroids have "emetic" properties, which might be explained by their direct stimulation of area postrema. It is known that estrogens increase the brain's excitability. Another possible mechanism could be by interacting with liver metabolism, resulting in the production of irregular metabolites, which in turn possess "emetic" qualities.