Etiology Causes 1. Endometrial abnormality Scared or poorly vascularized endometrium in the corpus 2) Curettage, Delivery, cs and infection of endometrium Placental a normality Large placenta(multiple pregnancy), succenturiate lobe(副胎盘) 3. Delayed development of trophoblastEtiology • Causes 1. Endometrial abnormality 1) Scared or poorly vascularized endometrium in the corpus. 2) Curettage, Delivery, CS and infection of endometrium 2. Placental abnormality Large placenta (multiple pregnancy), succenturiate lobe (副胎盘) 3. Delayed development of trophoblast