Placenta accreta spectrum (PAS) is one of the most severe obstetric complications, threatens maternal life because of massive hemorrhage during delivery. The major diagnostic method for PAS was ultrasonic inspection or MRI. However, ultrasound and MRI only have effective diagnostic value in the third trimester. There is few efficient circulating biomarkers was reported to predict PAS. In this project, we expect to identify ncRNA biomarkers as well as other molecular biomarkers to predict PAS.