Early prediction of placenta accreta spectrum in women with prior cesarean delivery using transvaginal ultrasound at 11 to 14 weeks

Background: There is a growing body of evidence that sonographic signs of placenta accreta spectrum can be observed in the first trimester of pregnancy. The most significant marker is placental location next to or in the scar niche in women with a prior cesarean delivery. Objective: This study aimed to assess the performance of transvaginal ultrasound in the early prediction of placenta accreta spectrum in women with a prior cesarean delivery. Study Design: This was a retrospective cohort of women with a history of cesarean delivery who had transvaginal ultrasound at 11 to 14 weeks’ gestation between September 2016 and May 2018. Ultrasound reports were reviewed and graded for suspicion of placenta accreta spectrum as follows: Grade 0 (no suspicion) if the placenta is not next to the scar; Grade 1 (intermediate suspicion) if the placenta is next or on the scar; Grade 2 (high suspicion) if the placenta was inside the scar niche. In addition, all images were reviewed and graded by trained specialists blinded to the outcome. The primary outcome was a histologic diagnosis of placenta accreta spectrum. Sensitivity, specificity, positive predictive value, and negative predictive value of first-trimester transvaginal ultrasound to detect placenta accreta spectrum were assessed. Results: In this study, 467 patients were included, and 8 (1.7%) had placenta accreta spectrum at delivery. Using the original report, 442 patients (94.6%) were Grade 0, 20 (4.3%) Grade 1, and 5 (1.1%) Grade 2. The revised grading had 456 patients (97.6%) with Grade 0, 5 (1.1%) with Grade 1, and 6 (1.3%) with Grade 2. Patients with Grade 2 yielded a sensitivity of 62.5% (95% confidence interval, 24.5–91.5), specificity of 100% (95% confidence interval, 99.2–100.0), positive predictive value of 100% (95% confidence interval, 97.0–100.0), and negative predictive value of 99.4% (95% confidence interval, 98.4–99.7). Any sonographic suspicion of placenta accreta spectrum (Grade 1 or Grade 2) had a sensitivity of 75% (95% confidence interval, 34.9–96.8), specificity of 95.9% (95% confidence interval, 93.6–97.5), positive predictive value of 24% (95% confidence interval, 14.8–36.4), and negative predictive value of 99.6% (95% confidence interval, 98.5–99.9). The blinded image review yielded a better specificity (99.1% vs 95.9%; P=.001) and a positive predictive value (63.6% vs 24%; P=.02) with similar sensitivity (87.5% vs 75%; P=.52) and negative predictive value (99.8% vs 99.6%; P=.55). Conclusion: Transvaginal ultrasound between 11 and 14 weeks’ gestation in women a with prior cesarean delivery can identify at least 3 of 4 cases of placenta accreta spectrum. A finding of placental implantation within the scar niche has high positive predictive value for placenta accreta spectrum. Prospective studies are needed to assess routine screening for placenta accreta spectrum at 11 to 14 weeks’ gestation in women with a prior cesarean delivery.