This in turn prevents effective uterine contractions, and leads to uterine atony.

胎盘组会阻子宫的有效收缩，而导致宫缩乏力。

The amount of bleeding can vary, and it can be intermittent or continuous, sometimes increasing during labor because of uterine contractions and cervical dilation.

出量不等，可能是间断或连续出，有时在生产时由于宫颈扩张，出量会增多。

Power refers to forceful uterine contractions, passenger refers to the fetus, and passage refers to the route that the fetus has to travel through the bony pelvis.

产力指有力的子宫收缩，娩出物指胎儿，产道指胎儿穿过骨盆的路径。

It can also occur when a woman is unable to empty her bladder, since a full bladder can push against the uterus and interfere with uterine contractions.

不仅如此，膀胱排空能引起产后子宫收缩乏力，因为充盈的膀胱将推挤子宫，进而阻子宫的有效收缩。

Finally, some commonly used obstetric medications such as anesthetics (especially halothane), magnesium sulfate, nifedipine, and terbutaline can all interfere with uterine contractions and increase the risk of uterine atony.

此外，一些产科常用药物如麻醉药（特别是氟烷）、硫酸镁、硝苯地平和特布他林等会影响产后子宫的正常收缩，增加宫缩乏力的风险。