The diagnosis of PE is strictly followed by the guidelines issued by the American College of Obstetricians and Gynecologists. Placental tissue is collected from the placental villi (avoiding arteries and calcified areas) immediately after delivery and is repeatedly gently cleaned with phosphate buffers. Samples should be stored in 4% formaldehyde or immediately frozen at -80℃ for subsequent analysis. There are a total of 6 placental tissue samples, including 3 from the preeclampsia (PE) group and 3 from the healthy control group.