Alright, as a quick recap, placenta previa describes a placenta that's in the lower uterus instead of the upper uterus.

好！快速回顾一下：前置胎盘指的是胎盘生长在子宫下部，而非如正常情况下在子宫上部。

Placenta previa is often diagnosed during prenatal ultrasounds, but occasionally it's not recognized until cervical changes during labor cause bleeding to happen.

产前超声检查可以确诊前置胎盘，也有部分在生产时因不明原因流血才发现。

In fact, endometrial damage from things like a previous cesarean section, an abortion (which could be induced or spontaneous), uterine surgery, and multiparity or multiple pregnancies can all decrease vascularization and increase the risk of placenta previa.

事实上，类似先前有剖腹产、人工流产、子宫手术或者多胎多次怀孕史等均可造成子宫内膜损伤都有可能影响子宫内膜血管的生成，增加前置胎盘的风险。