This separation is usually caused by degeneration of the uterine arteries that supply blood to the placenta typically from chronic problems like smoking or hypertension.

这种剥离经常是由于给胎盘供血的子宫动脉的退化，通常是由吸烟或高血压等慢性问题引起的。

The maternal layer, the decidua basalis, is literally a flattened out bag of blood with uterine arteries delivering blood in and uterine veins pulling blood out.

所谓“母体层”，即基蜕膜，就是一个平整的血袋，将子宫动脉的血输送进去。