The objectives, design and implementation of the INTERGROWTH-21st Project - Villar, J; Altman, D; Purwar, M; Noble, J; Knight, H; Ruyan, P; Cheikh Ismail, L; Barros, F; Lambert, A; Papageorghiou, A; Carvalho, M; Jaffer, Y; et al. (S. Karger AG, 2014)