Initially there is descent, which is the downward movement of the fetus to the pelvic inlet.

起初是下降，胎儿向下移动进入骨盆入口。

In this position, the smallest diameter (which is referred to as the suboccipitobregmatic diameter) presents at the pelvic inlet.

在这个姿势下，以最小的直径（指枕下前囟径）出现在骨盆入口。

Finally, there's fetal presentation which refers to the first fetal part, called the presenting part, to descend into the pelvic inlet.

最后，胎先露，指胎儿最先下降入骨盆入口的部分，称为先露部分。

The fetus moves from the pelvic inlet (which is about minus 5 station) down to the ischial spines (which is station 0), and this position's called engagement.

胎儿从骨盆入口（-5）向下到坐骨棘（0），这个位置称为衔接。

Next there's internal rotation, where the fetal shoulders internally rotate by 45 degrees so the widest part of the shoulders are in line with the widest part of the pelvic inlet.

接下来是内旋转，胎儿的肩部向内旋转45度，以便肩部最宽的部分与骨盆入口最宽的部分在一条线上。