Diagnostic accuracy of first‐trimester ultrasound in detecting abnormally invasive placenta in high‐risk women with placenta previa

Abstract

To ascertain the diagnostic accuracy of ultrasound in detecting AIP during the first trimester (11-14 weeks of gestation) of pregnancy in women at risk of these conditions. Retrospective analysis on prospectively collected data on women at risk for AIP based upon the presence of at least one prior CS and/or uterine surgery and placenta previa who had an ultrasound assessment for AIP since the 11-14 weeks scan. The ultrasound signs explored in the present study were: loss of clear zone, placental lacunae, bladder wall interruption, uterovescical hypervascularity. The potential of ultrasound and different ultrasound signs to predict the different types of AIP was assessed computing the summary estimates of sensitivity, specificity, diagnostic odd ratio, positive and negative likelihood ratios. One hundred and eighty-eight women with placenta previa and at least one previous caesarean section or uterine surgery were included in the study. All the ultrasound signs explored where significantly associated with the occurrence of AIP. Overall, ultrasound had a sensitivity of 84.3% (95% CI 74.7-91.4), a specificity of 61.9 (95% CI 51.9-71.2), a DOR of 8.6 (95% CI 4.1-19.3), a LR+ of 2.2 (95% CI 1.7-2.9) and a LR- of 0.3 (95% CI 0.1-0.4) in detecting AIP, when at least one ultrasound sign was used to make the diagnosis. Using two ultrasound signs to label a case as positive, increased the diagnostic accuracy in terms of specificity, while it did not affect sensitivity. Among the different ultrasound signs, the loss of the clear zone had a sensitivity of 84.4% (95% CI 74.7-91.4) and a specificity of (81.9% (95% CI 73.2-88.7) in detecting AIP, while the corresponding figures for placental lacunae and bladder wall interruption were 78.3% (95% CI 67.9-86.6) and 75.9% (95% CI 65.3-84.) and 81.0% (95% CI 72.1-88.0) and 99.1 (95% CI 94.8-100) respectively. The optimal combination of sensitivity and specificity was achieved when at least two imaging signs of AIP were used in the diagnostic algorithm. AIP can be detected since the first trimester of pregnancy in women at risk for this condition and that ultrasound performed between 11 and 14 weeks of gestation has an overall good diagnostic accuracy for detecting all types of AIP. However, these findings are applicable only to women with major placenta previa and prior uterine scar.