Cross-Country Individual Participant Analysis of 4.1 Million Singleton Births in 5 Countries with Very High Human Development Index Confirms Known Associations but Provides No Biologic Explanation for 2/3 of All Preterm Births. - Ferrero DM; Larson J; Jacobsson B; Di Renzo GC; Norman JE; Martin JN Jr; D'Alton M; Castelazo E; Howson CP; Sengpiel V; Bottai M; Mayo JA; et al. (PloS one, 2016)