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3
rd
stage of labour :
Signs of placental separation
 A fresh show of blood from vagina,
 The umbilical cord lengthens outside the
vagina,
 The fundus of the uterus rises up,
 The uterus becomes firm and globular.

Engagement?

Position?
Atitude ?
Station?
Moulding ?
Important terms in obstetrics

LOT
right left
Left Occipito -Transverse position

the position of the presenting part

Engagement (and stations of fetal head during
delivery)

Normal L abour / 3

rd
Lecture
Mechanism of L abour

Reference T extbook

Dr. Suhaila Al -Shaikh Obstetrics by ten teachers
20 th ed (2017 ): ch 12 ; p 386 -89

Learning objectives

To understand the cardinal movements of
the fetal head when it passes through the
maternal pelvis and the effect of maternal
pelvis asymmetry and fetal skull asymmetry
in directing these movements

Mechanisms of labor, or the

cardinal movements of labor,
refer to the changes in
position and attitude that the
fetal head undergoes during
its passage through the birth
canal.

In normal labour

( i.e : for the vertex presentation and the
gynaecoid pelvis).
The relation of the fetal head and fetal body to
the maternal pelvis changes as the fetus
descends through the pelvis.
To get the optimal diameters of the fetal skull
while it descends through the birth passage

The movements arranged in

order:
 Engagement
 Descent
 Flexion
 Internal rotation
 Extension
 External rotation and restitution
 Delivery of anterior and posterior shoulders
 Expulsion of the rest of the body

Engagement - 1

Engagement is descent of the
biparietal diameter of the fetal
head below the plane of the
pelvic inlet.
The head enters the pelvis in the
occiput transverse position in
women with a gynecoid pelvis.

Engagement (and stations of fetal head during

delivery)

DESCENT: - 2

 When the uterus contract it
pushes the baby down through
the birth canal ( the fetal head
descend through the pelvic
brim to the midcavity ).

3 - Flexion

Uterine activity is fundally dominant;
the line of force is down the fetal
spine and causes flexion of the
fetal head. flexion is a passive
movement that permits the
smallest diameter of the fetal head
(suboccipitobregmatic diameter) to
be presented to the maternal
pelvis.

With the progress at the

end of the first stage and
beginning of the 2
nd
stage
there is further descent &
flexion of the presenting
part (head) in the pelvis

Internal rotation - 4

The head rotates from the
left occipito - transverse
position at engagement to
become direct occipito -
anterior position .

Internal rotation of the head. (a) Inlet: right

occipitotransverse position. (b) Mid -cavity: right
occipitoanterior position. (c) Outlet: direct
occipitoanterior position

Further descent through the

pelvis causes the chin to be
forced tightly up against the
fetal chest.

Extension - 5

As the head continues its descent,
The fetal occiput comes to lie
behind the maternal symphysis
pubis, gradual extension of the
fetal head occurs distending the
perineum

With more extension, the widest

diameter passes through the
vulval introitus (crowning) and
the head is born by extension at
the fetal neck.

Extension

Restitution and external - 6
rotation

As the head is being born , the shoulders

enter the maximum diameter (the
transverse diameter) of the maternal
pelvic inlet. As they descend through the
canal, the shoulders rotate (just as the
head did in internal rotation) and, as they
do so, the head (outside the body now)
rotates 90 ° . The shoulders now lie in the
anteroposterior diameter behind the
maternal symphysis pubis.

Delivery of the body - 7

Delivery of the anterior shoulder is
aided by gentle downward traction
on head. The posterior shoulder is
then delivered by gentle upward
traction on the head. Following
these maneuvers, the body, legs,
and feet are delivered with gentle
traction on the shoulders.

features of normal labour ?

1 . Spontaneous onset at 37 – 42 weeks’ gestation.
2 . Singleton pregnancy.
3 . Cephalic vertex presentation.
4 . No artificial interventions.
5 . Cervical dilatation of at least 1 cm every 2 hours
in the active phase of first stage .
6 . Active second stage no more than 2 hours in
primiparous and 60 minutes in multiparous
woman.
7 . Spontaneous vaginal delivery.
8 . Third stage lasting no more than 30 minutes
with active management.


رفعت المحاضرة من قبل: Hatem Saleh
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