求翻译：流产时的病理变化多数是胚胎及胎儿先死亡，随后发生底蜕膜出血或胎盘后出血形成血肿，造成妊娠物与子宫剥离，犹如异物引起宫缩而被排出。有时底蜕膜海绵层出血坏死或有血栓形成也会促使胎儿死亡。是什么意思？

The pathological changes most when abortion is embryonic and fetal death, end of subsequent formation of decidual bleeding or bleeding after placental hematoma, resulting in pregnancy and uterine split as if foreign bodies caused by uterine contractions and was discharged. Sometimes hemorrhagic necrotic decidua basalis sponge layer or thrombosis can cause fetal death.