b. Fetus in the Vertex Position. The fetus in the vertex position makes seven
adaptations or cardinal movements. Refer to figure 10-6.
(1) Descent. The fetus head is pushed deep into the pelvis in a sideways
position, the face is to the left and the occiput is to the right.
(a) In a primigravida, this may occur two weeks before delivery. This is
referred to as "lightening." Lay people might call this "dropping."
(b) In a multipara, this may not occur until dilatation of the cervix.
(2) Flexion. As the fetus head descends, the chin is flexed to come into
contact with the infant's sternum. The occiput position allows the occipital bone in the
back of the head to lead the way (smallest diameter of the head).
(3) Engagement. This is when the presenting part is at the level of the
ischial spines or at a zero (0) station. Before this time, it is referred as "floating."
(a) The amount of internal rotation depends on the position of the fetus
and the way the head rotates to accommodate itself to the changing diameters of the
(b) If the fetus starts to descend in LOA or LOT, rotation is only a short
distance-45 to 90 degrees.
If the head is in a posterior position, it may mean a turn of 180
(d) Occasionally, the fetus may not turn to the anterior position and is
born O.P. (occiput posterior).
(5) Extension. As the previously flexed head slips out from under the pubic
bone, the fetus is forced to extend his head so that the head is born pushing upward out
of the vaginal canal. The natural curve of the lower pelvis and the baby's head being
pushed outward forces distention of the perineum and vagina. As it moves through the
vaginal canal, the chin lifts up (extends) and the head is delivered. During this
maneuver, the fetal spine is no longer flexed, but extends to accommodate the body to
the contour of the birth canal.
External rotation restitution.
(a) Once the fetus head is out, it will turn to line up with its back,
revealing its position just before internal rotation of the head. This is called restitution.