The placenta is a transient, extra-embryonic organ primarily regulated by the fetal genome and shared between mother and fetus. For these reasons, the epigenetic mechanisms regulating gene expression within the placenta may not be under the same constraints as other organs. DNA methylation studies in the placenta are complicated by the different cell types that make up the placenta, each with their own unique DNA methylation profile. The placenta methylome is also hypomethylated in comparison to other organs within the body and these hypomethylated regions occur in large domains, however the reasons for this are unclear. We are using cutting-edge technologies to identify the epigenetic modifications involved in gene regulation in the placenta, how they change across gestation and in pregnancy complications.