USMLE Step 2 CK Lecture Notes 2019: Obstetrics/Gynecology (Kaplan Test Prep)

rate of dilation is slow, but at 6 cm of dilation, the rate accelerates to a maximum
rate in the active phase of labor. Complete dilation is expressed as 10 cm.

Cardinal Movements of Labor. The first three steps occur simultaneously.

The next four steps occur in order.

Engagement: movement    of  the presenting  part    below   the plane   of  the pelvic

inlet

Descent:    movement    of  the presenting  part    down    through the curve   of  the birth

canal

Flexion:    placement   of  the fetal   chin    on  the thorax

Internal    rotation:   rotation    of  the position    of  the fetal   head    in  the mid pelvis

from    transverse  to  anterior-posterior

Extension:  movement    of  the fetal   chin    away    from    the thorax

External    rotation:   rotation    of  the fetal   head    outside the mother  as  the head

passes  through the pelvic  outlet

Expulsion:  delivery    of  the fetal   shoulders   and body