OECD Countries

Expanding the review to OECD countries may increase eligible studies while retaining enough comparability for synthesis. The review focuses on OECD countries to improve comparability while broadening the evidence base beyond UK-only reviews. Eligible studies must involve women and babies born in countries that were OECD members at the time of the study. The search strategy will not restrict by country despite OECD-only eligibility to avoid missing relevant papers.