DNA methylation is a chemical change to our DNA that influences the extent to which our genes are expressed. Environmental factors can affect DNA methylation. DNA methylation has previously been used to accurately predict age, and the difference between a person's age and the age predicted by their DNA methylation has been shown to be associated with mortality and various health outcomes. Recently, this approach has also been used to identify a set of DNA methylation markers that predict gestational age at birth. This measure of DNA methylation gestational age has been shown to be associated with birth weight, independently of gestational age, sex and ancestry. In this project, we will look at whether maternal factors such as maternal smoking, alcohol use, age, and educational level are associated with DNA methylation gestational age, and we will assess the association of DNA methylation gestational age with childhood growth trajectories.