Preterm birth (PTB) represents a major problem for modern obstetrics due to its increasing frequency and the accompanying socioeconomic impact. As stress and depression are major causes of premature births, such conditions could alter the epigenome and thus aff ect long-term health in the victims. We performed a relatively large epigenome-wide association study (EWAS) on PTB using genome-wide DNA methylation data. The study samples consist of 73 pairs of indetical twins aged from 30 to 36 who have their gestational ages (33-42 weeks) recorded by The Danish Medical Birth Registry. Among them, there are 25 preterm birth pairs with gestational age