胎盘移行 Gestational age at Previa or hemorrhage sonography(wk) at delivery (%) <20 2.3 20-25 3.2 25-30 5.2 30-35 24胎盘移行 Gestational age at sonography(wk) Previa or hemorrhage at delivery (%) <20 20-25 25-30 30-35 2.3 3.2 5.2 24