Many researchers are focusing on epigenetic regulation in the placenta. Because the proper development and function of the placenta are crucial for the normal healthy growth and survival of the developing fetus, the study of epigenetic alterations is providing critical insights into the biology of fetal development and the pathogenesis of complications in pregnancy. One epigenetic alteration is genomic imprinting. Alleles from both the father and mother are necessary for normal human and placental development. For example, the paternally expressed IGF2 gene and maternally expressed H19 gene are located in 11p15.5 and they are coordinately regulated by differentially methylated regions (DMRs). The main phenotype of Silver-Russell syndrome is severe fetal growth retardation (FGR) that is caused by a reduction in IGF2 transcription as a result of a loss of methylation at the H19 DMR. Hypermethylation at the H19 DMR is found in 30% of cases of Beckwith-Wiedemann syndrome and the overgrowth phenotype. The other main mechanism is a promoter DNA methylation. Hypomethylation of a promoter of the SERPINA3 gene in the placenta is associated with FGR and preeclampsia. These clues to the epigenetic phenomena involved in the processes of human development and disease in pregnancy have been found in recent years.