Sometimes the several-hours after delivery is called the " fourth stage" , because there are major physiologic changes like adaption to the blood loss, and the start of uterine involution, where the uterus begins returning to its pre-pregnant state.

有时分娩后几个小时称为“第四产程”，因为有很多重要的生理变化，例如血液流失的适应，以及子宫复旧的开始，子宫回到产前的状态。