Twin pregnancy increases the risk of maternal and fetal complications, which include gestational hypertension, premature labor, twin-to-twin transfusion syndrome, intrauterine growth restriction, anemia, amniotic fluid abnormalities. Comprehensively understanding the molecular mechanisms of the disease and identification of markers contribute to development of novel therapeutic approaches. In addition, the twin pregnancy, especially the monochorionic, is an essential model of experiments of nature. This model can be applied to distinguish the epigenetic differences of twins in utero and after birth in the same genomic context. The aim of the study is to constitute a prospective cohort of twin pregnancies and the offspring.