Currently, many a priori indexes are being used to assess maternal adherence to the Mediterranean diet (MD) during pregnancy but each with different components, cut-off points, and scoring systems. This narrative review aimed to identify all observational studies utilizing a priori indexes to assess maternal adherence to the MD during pregnancy. A systematic search was conducted in Pubmed until 1 July 2020. Among the 27 studies included, eight different a priori indexes were identified. Studies included a range of 5 to 13 dietary components in their indexes. Only three dietary components-vegetables, fruits, and fish-were common among all indexes. Dairy and alcohol were the only two components modified for pregnancy. All but one study either excluded alcohol from their index or reversed its scoring to contribute to decreased adherence to the MD. Approximately half of the studies established cut-off points based on the distribution of the study population; the others utilized fixed criteria. This review emphasizes the incongruent definitions of the MD impairing effective comparison among studies relating to maternal or offspring health outcomes. Future research should carefully consider the heterogeneous definitions of the MD in a priori indexes and the relevance of incorporating pregnancy-specific nutritional requirements.
Keywords: Mediterranean diet; a priori index; maternal nutrition; nutrition assessment; pregnancy.