Identifying genetic and epigenetic markers for fetal growth variation is important for both perinatal and adult health. Imprinted genes, which show parent-of-origin, specific, monoallelic expression, play key roles in fetal growth. There have been several genome-wide association studies to link genetic variants with birth weight, although none of them assumed parent-of-origin inheritance pattern, mainly because it requires large family cohorts to impute parental origin of the variants. As a recent collaborative project with the ALSPAC, we have shown that the maternal inheritance of a single copy number variant (repeat sequence 1: RS1) in the promoter of imprinted PHLDA2 gene to be significantly associated with increased birth weight and head circumference1. We hypothesise that there will be more genetic variants associated with fetal growth to be identified if parental origin of the allele is taken into account. Therefore, we would like to carry out a genome-wide search for genetic variants in assocition with fetal growth considering parental origin effects. Importantly, monoallelic expression of imprinted genes is controlled by differential DNA methylation established during gametogenesis. We propose to carry out a study using existing genomic, epigenomic, expression and phenotypic data at the ALSPAC to find genes important in fetal growth using a parent-of-origin model.