Background: Placenta accreta spectrum (PAS) is a life-threating complication in the field of obstetrics. Sometimes we face with unexpected PAS cases which is potentially higher maternal mortality and morbidity compared with expected cases. The present study was conducted to examine the prevalence of PAS and to elucidate its risk factors using a large Japanese birth cohort study. Methods: We reviewed the results of a nationwide prospective birth cohort study in Japan, and identified 90,554 participants treated from 2011 to 2014 in 15 regional centers. Multiple regression models were created to identify the risk factors for PAS. These data were obtained from self-reported questionnaires or patient medical records. Results: This analysis consisted of 202 cases of PAS (18 with placenta previa and 184 without placenta previa) and 90,352 cases without PAS. The multiple logistic regression analysis showed that placenta previa (adjusted odds ratio [aOR]: 12.86, 95% confidence interval [CI] 7.70-21.45, P < 0.001), assisted reproductive technology-related pregnancies (aOR: 6.78, 95% CI 4.54-10.14, P < 0.001), smoking during pregnancy (aOR: 1.95, 95% CI 1.15-3.31, P = 0.013), more than two previous cesarean sections (aOR: 2.51, 95% CI 1.35-4.67, P = 0.004), and uterine anomalies (aOR: 3.97, 95% CI 1.24-12.68, P = 0.020) increased the risk of PAS. Conclusion: In general population, placenta previa, assisted reproductive technology-related pregnancy, smoking during pregnancy, repeated cesarean sections, and uterine anomalies were risk factors for PAS in the Japanese population.
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