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

OBJECTIVE: To elucidate the risk factors, histopathological correlations and diagnostic accuracy of prenatal imaging in pregnancies complicated by posterior placenta accreta spectrum (PAS) disorders.

METHODS: MEDLINE, EMBASE and CINAHL were searched for studies reporting on women with posterior PAS. Inclusion criteria were women with posterior PAS confirmed either at surgery or on histopathological analysis. The outcomes explored were risk factors for posterior PAS, histopathological correlation and the diagnostic accuracy of ultrasound and magnetic resonance imaging (MRI) in detecting posterior PAS. Random-effects meta-analysis of proportions was used to analyze the data.

RESULTS: Twenty studies were included. Placenta previa was present in 92.8% (107/114; 17 studies) of pregnancies complicated by posterior PAS, while 76.1% (53/88; 11 studies) of women had had prior uterine surgery, mainly a Cesarean section (CS) or curettage and 82.5% (66/77; 10 studies) were multiparous. When considering histopathological analysis in women affected by posterior PAS, 77.5% (34/44; 11 studies) had placenta accreta, 19.5% (8/44; 11 studies) had placenta increta and 9.3% (2/44; 11 studies) had placenta percreta. Of the cases of posterior PAS disorder, 52.4% (31/63; 12 studies) were detected prenatally on ultrasound, while 46.7% (32/63; 12 studies) were diagnosed only at birth. When exploring the distribution of the classic ultrasound signs of PAS, placental lacunae were present in 39.0% (12/30; seven studies), loss of the clear zone in 41.1% (13/30; seven studies) and bladder-wall interruption in 16.6% (4/30; seven studies) of 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% (26/32; 11 studies) of cases were detected on prenatal MRI, while 26.5% (6/32; 11 studies) were discovered only at the time of CS.

CONCLUSIONS: Placenta previa, prior uterine surgery and multiparity represent the most commonly reported risk factors for posterior PAS. Ultrasound had a very low diagnostic accuracy in detecting these disorders prenatally. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.