Many theories have been proposed over the years to explain the sequence of events that culminate in labor and delivery, but the exact metabolic and endocrine pathway are not yet known.

• 分娩发动的原因目前尚不清楚，分娩是一个复杂的生理活动，分娩发动必备的条件是胎儿的成熟和母体的准备，可能与下列学说有关。