| Summary: | OBJECTIVE: To test an objective ultrasound marker for diagnosing the presence and severity of abnormally invasive placenta. METHODS: Women at risk of abnormally invasive placenta underwent a three-dimensional power Doppler ultrasound scan. The volumes were examined offline by a blinded observer. The largest area of confluent three-dimensional power Doppler signal (Area of Confluence [Acon], cm2) at the uteroplacental interface was measured and compared in women subsequently diagnosed with abnormally invasive placenta and women in a control group who did not have abnormally invasive placenta. Receiver operating characteristic curves were plotted for prediction of abnormally invasive placenta and abnormally invasive placenta requiring cesarean hysterectomy. RESULTS: Ninety-three women were recruited. Results were available for 89. Abnormally invasive placenta was clinically diagnosed in 42 women; 36 required hysterectomy and had abnormally invasive placenta confirmed histopathologically. Median and interquartile range for Acon was greater for abnormally invasive placenta (44.2 [31.4–61.7] cm2) compared with women in the control group (4.5 cm2 [2.9–6.6], P<.001) and even greater in the 36 requiring hysterectomy (46.6 cm2 [37.2–72.6], P<.001). Acon rose with histopathologic diagnosis: focal accreta (32.2 cm2 [17.2–57.3]), accreta (59.6 cm2 [40.1–89.9]), and percreta (46.6 cm2 [37.5–71.5]; P<.001 analysis of variance for linear trend). Receiver operating characteristic analysis for prediction of abnormally invasive placenta revealed that with an Acon of 12.4 cm2 or greater, 100% sensitivity (95% confidence interval [CI] 91.6–100) could be obtained with 92% specificity (95% CI 79.6–97.6); area under the curve is 0.99 (95% CI 0.94–1.0). For prediction of abnormally invasive placenta requiring hysterectomy, 100% sensitivity (95% CI 90.3–100) can be obtained with an Acon of 17.4 cm2 or greater with 87% specificity (95% CI 74.7–94.5; area under the curve 0.98 [0.93–1.0]). CONCLUSION: The marker Acon provides a quantitative means for diagnosing abnormally invasive placenta and assessing severity. If further validated, subjectivity could be eliminated from the diagnosis of abnormally invasive placenta. LEVEL OF EVIDENCE: II
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