Please cite this paper as: Bustamante M, Danileviciute A, Espinosa A, Gonzalez JR, Subirana I, Cordier S, Chevrier C, Chatzi L, Grazuleviciene R, Sunyer J, Ibarluzea J, Ballester F, Villanueva CM, Nieuwenhuijsen M, Estivill X, Kogevinas M. Influence of fetal glutathione S-transferase copy number variants on adverse reproductive outcomes. BJOG 2012;119:11411146. A nested casecontrol association study was designed to investigate the influence of maternal and fetal copy number variants (CNVs) on reproductive outcomes. Genotypes of ten CNVs encompassing GST and CYP genes were assessed. Significant associations were only found for child CNV genotypes. In particular, the child GSTM1 insertion allele was associated with prematurity protection (odds ratio, 95% CI: 0.67, 0.510.89; P < 0.01), whereas the child GSTT2B insertion allele was associated with an increased risk of being small for gestational age (odds ratio, 95% CI: 1.33, 1.071.67; P = 0.01). The study highlights the role of the fetal genome in prenatal development and also the need to analyse CNVs in a systematic manner.