Risk factors, histopathology and diagnostic accuracy in posterior placenta accreta spectrum disorders: systematic review and meta-analysis

OBJECTIVES: To elucidate the risk factor, histopathological correlations and diagnostic accuracy of prenatal imaging in detecting posterior PAS.METHODS: MEDLINE, Embase and CINAHL were searched. Inclusion criteria were women with posterior PAS confirmed either at surgery or histopathological analysis. The outcomes explored were: risk factor for posterior PAS, histopathological correlation, and diagnostic accuracy of ultrasound and MRI in detecting these anomalies. Random-effect meta-analyses of proportions and summary estimates of sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) and diagnostic odds ratio (DOR) using the hierarchical summary receiver-operating characteristics (HSROC) model were used to analyse the data.RESULTS: 20 studies were included. Placenta previa was present in 92.8% pregnancies complicated by posterior PAS, while 76.1% of women had a prior uterine surgery (11 studies, 53/ 88 women), mainly a CS or curettage. When considering the histopathological analysis of women affected by posterior PAS, 77.5% had placenta accrete (11 studies, 34/44 women), 19.5% placenta increta (11 studies, 8/44 women)and 9.3% placenta percreta (11 studies, 2/44 women). 56.4% of posterior PAS disorders were detected prenatally on ultrasound, while 46.7% were diagnosed only at birth (12 studies, 31 /63 women). When exploring the distribution of the classic ultrasound signs of PAS, placental lacunae were present in 39.0% (7 studies, 12/30 women), loss of the clear zone in 41.15% (7 studies, 13/30 women) and bladder wall interruption in 16.6% of women (7 studies, 4/30 women), while none of the included cases showed hypervascularization at the bladder wall interface. When assessing the role of MRI in detecting posterior PAS, 73.5% of cases were detected at prenatal MRI, while 26.5% were discovered only at the time of CS (11 studies, 26/32 women).CONCLUSION: Placenta previa and prior uterine surgery represent the most commonly reported risk factors for posterior PAS. Ultrasound had a very low diagnostic accuracy in detecting these disorders prenatally. This article is protected by copyright. All rights reserved.