To evaluate the diagnostic performance of third trimester ultrasound for the diagnosis of clinically significant Placenta accreta spectrum disorder (PAS) in women with a low-lying placenta (less than 20 mm from the internal cervical os) or placenta praevia (covering the os) METHODS: Pregnant women with a low-lying placenta or placenta praevia, age ≥ 18 years and gestational age at ultrasound ≥ 26+0/7 weeks of gestation were prospectively included in the study. Ultrasound suspicion of PAS was raised in the presence of at least one of these signs: (1) obliteration of the hypoechoic space between the uterus and the placenta; (2) interruption of the hyperechoic interface between the uterine serosa and the bladder wall; (3) abnormal placental lacunae. In order to assess the ability of ultrasound to detect clinically significant PAS, a composite outcome comprehensive of both active management at delivery and histopathological confirmation of PAS was considered as the reference standard. PAS was considered of clinical significance if, in addition to histological confirmation, at least one of these procedures was carried out after delivery: use of hemostatic intrauterine balloon, compressive uterine suture, peripartum hysterectomy, uterine/hypogastric artery ligation, uterine artery embolization.
