Study Selection
The primary outcome of this systematic review is excessive or inadequate gestational weight gain according to the NAM recommendations, and secondary outcomes include GDM, pre-eclampsia, preterm birth, delivery mode and birth weight. Studies were included if they met the following criteria: 1) Prospective cohort studies of women in the preconception period or pregnancy recruited from the general population. 2) Diet quality measured with pre-specified scoring scales and validated dietary assessment methods. 3) Assessment of the association between diet quality score and any of the systematic review outcomes. The publications identified with the search process were uploaded to the Covidence software. YY and IH independently screened the titles and abstracts. All references that met the inclusion criteria or those for which eligibility was uncertain were selected for full-text screening. Reasons for exclusion at the time of full-text screening were recorded. Any disagreements arising during the selection process were resolved by discussion with a third reviewer (LD). The process of study selection is reported using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram28.