Preventing preterm births: trends and potential reductions with current interventionsin 39 very high human development index countries - Chang, H H; Larson, J; Blencowe, H; Spong, C Y; Howson, C P; Cairns-Smith, S; Lackritz, E M; Lee, S K; Mason, E; Serazin, A C (Lancet, 2013)