Third-trimester ultrasound for antenatal diagnosis of placenta accreta spectrum in women with placenta previa: results from the ADoPAD study

Objectives: 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. Results: A total of 568 women underwent transabdominal and transvaginal ultrasound examinations. Of them, 95 delivered in local hospitals and placental pathology according to the study protocol was therefore not available. Among the 473 for whom placental pathology was available, clinically significant PAS was diagnosed in 99 (21%). A normal hypoechoic space between the uterus and the placenta reduces post-test probability of PAS from 21% to 5% in women with a low-lying placenta or placenta previa in the third trimester of pregnancy, and from 62% to 9% in the subgroup of women with previous cesarean section and anterior placenta. The absence of lacunae reduces post-test probability of PAS from 21% to 9% in women with low-lying placenta or placenta previa in the third trimester of pregnancy, and from 62% to 36% in the subgroup with previous cesarean section and anterior placenta. On the other side, when lacunae are seen the post-test probability increases from 21% to 59% in the whole study population and from 62% to 78% in women with placenta previa, previous cesarean section and anterior placenta. Conclusions: Grey-scale ultrasound is a good test to identify pregnancies at low risk of PAS in this high risk population. Ultrasound can be safely used to guide management decisions, concentrating greater resources in patients with the higher risk of clinically significant PAS This article is protected by copyright. All rights reserved.