Search strategy
Four databases of published literature (MEDLINE ALL (Ovid), Embase
(Ovid), Food Science and Technology Abstracts (Ovid) and CINAHL
(EBSCOHost)) were searched from database creation to the cut-off date of
March 5th2020. Both medical subject headings and text
keywords were used to develop a comprehensive search strategy with
inputs from the whole research team including the health science
librarian (LS)26. Two groups of keywords were used:
‘preconception or pregnancy’, and ‘diet quality’ (See Table S1 for
detailed search terms used in OVID Medline). The reference lists of
included studies and relevant review articles were screened to identify
any additional studies. When eligible abstracts were identified, the
title and authors were searched to determine if full-text articles had
been published. Eligibility was limited to full-text articles published
in scholarly peer-reviewed journals in English27.