illustration of mechanism of normal labor for medical students

1. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬

2. Normal labor
Definition of normal labor
Theories of onset of labor
Manifestations of onset of labor
Stages and mechanism of
normal labor

3. Definition of normal
labour
Spontaneous expulsion
Of full term ( 38 – 42 WK )
Living viable fetus ( single )
Presented by vertex
Through the natural passage
Within a reasonable time (not less than 3 h not more than 18 – 24 h )
Without complication for both mother and fetus

4. Normal
labor
Passenger Passage power
Uterine
contractions
Bearing
down effort

5. Theories of onset of normal labor
The cause of onset of labor is unknown however proposed theories include :
1- progesterone withdrawal.
2- prostaglandin release.
3- estrogen oxytocin effect .
4- placental oxytinase decrease.
5- uterine distention theory.
6- fetal cortisol theory.

6. Prodromal stages of labor
Last weeks of pregnancy before onset of labor
1- lightening
2- shelfing
3- pelvic pressure symptoms
4- increased vaginal discharge
5- false labor pains

7. Manifestations of onset of
labour
Symptoms
true labor pain
The bloody show
Signs
Abdominal examination
Vaginal examination

8. True labor pain
1- Involuntary rhythmic colicky
intermittent coordinated
uterine contractions
2-Start at the fundus with
gradually increasing frequency
and intensity
3-Retractions occur at the end
of each contractions leading to
descend of the presenting part
and dilatation of the cervix

9. Labor pain
False labor painsTrue labor pains
Irregular rhythmRegular rhythm
NotIncrease in frequency, duration and
intensity
Abdominal not referredAbdominal and referred to the back
Not effectiveEffective
Not bulgingMembrane bulging during contraction
RelivedNot relived by sedatives or anti
spasmodics.

10. Bloody show
Mucous stained with blood discharged from the vagina.

11. Signs
Abdominal examination
Abdominal wall becomes
rigid and tense during
uterine contractions
Between contractions it
relaxes making fetal
parts easily palpated
Vaginal examination
Cervical effacement
and dilatation
Bulging bag of
forewater

12. Stages of normal
labour
•From onset of labor
•To full dilatation of cervix
First
stage
•From full dilatation of cervix
•To full expulsion of the fetus
Second
stage
•Stage of expulsion of placenta
•Umblical cord and membranes
Third
stage

13. First stage
Stage of cervical effacement and dilatation
Duration:
in primigavidas 10-18 h
in multigravidas 6-10 h
Effacement:
Taking up the cervical canal in the
formation of the LUS
Degree of effacement:
Length in cm
Relative shortening
(30 % 50 %....)

14. Cervical dilatation
degree:
Finger bridth 1, 2,3,4,5( fully dilated )
In cm 2,4,6,8,10 ( fully dilated )
Degree in relation to full dilatation.

15. Causes of cervical effacement
and dilatation:
1- In late pregnancy cervix becomes dilatable
and soft due to edema and increased
vascularity( cervical ripening )
2- contractions of the longitudinal muscles of
the uterus which are inserted in the cervix
3- pressure on the cervix by bag of fore water
and presenting part.

16. Second stage
Start from full dilatation of the cervix and ends by complete expulsion of the fetus
Duration:
1-2h in primigravidas.
0.5 h in multigravidas.
Changes:
1- rupture of bag of fore water
2- uterine contractions and labor pains become stronger with
longer duration
3- full dilatation of cervix
4- desire to evacuate bladder and rectum
5- expulsion of the fetus is formed by:
bearing down 50% and uterine contractions 50%

17. Mechanism of delivery in normal labor
Delivery of the head
1- Descent
2- Engagement
3- Increased flexion
4- Internal rotation
5- Extension
6- Restitution
7- External rotation
Delevery of the shoulders and body

18. Delivery of the head
Descent
Continuous movement throughout labor due to:
1- Uterine contractions and retractions
2- Auxiliary force in the second stage of labor
3- straightening of the fetus by contractions and
retractions of the uterus

19. Engagement
- Passage of the widest
transverse diameter of the
presenting part through the
plane of the pelvic inlet
- In cephalic presentation
engagement occur when BPD
passes through the pelvic brim
- The leading part — the
vertex — is now near the level
of the ischial spines.

20. Delevery of the head
Increased flexion
Mechanism:
a) Head of fetus descends until
it reaches pelvic floor (levator-
ani).
b) Head of fetus pushes
against pelvic floor, so pelvic
floor stretches. By its elasticity,
pelvic floor recoils pushing
head of fetus upwards.

21. Delevery of the head
Increased flextion
Result:
- When flexion of the head of fetus is increased,
the antero-posterior diameter of the head of
fetus (related to pelvic cavity) will be the
smallest diameter which is suboccipito-
bregmatic (9.5 cm).
- Transverse diameter of the head of fetus is
biparietal diameter (9.5 cm).
- So, the part of fetal head related to pelvic
cavity will be circular, with a diameter of 9.5
cm.

22. Delevery of the head
Internal rotation
o Mechanism:
a) Uterine contractions and retraction (and other
forces) push the head of the fetus against the
levator muscle.
b) The head of fetus at this moment is a circle (9.5
cm diameter) in a circular plane (12.5 cm) [plane of
mid- cavity], so head can rotate.
c) The levator is directed forwards, downwards and
medially, so the head of the fetus rotates in the same
direction of levator

23. Delevery of the head
6-Internal rotation
Direction and degrees:
a) Direction of internal rotation is the same direction of levator
muscle [forwards, downwards and medially].
b) Degree:

24. Delevery of the head
Internal rotetion
N.B.;
→the anterior and posterior shoulders remain in their position
after internal rotation.
→Occiput becomes below symphysis pubis.

25. Delevery of the head
6-Extension
- Sub occipital region hinges below symphysis pubis, so occiput
becomes away from action of uterine contractions and retraction ( not
affected by them).
- By extension, head
of fetus comes out

27. Delevery of the head
Restitution
o When internal rotation occurs, the head rotates 45 degrees
downwards, forwards and medially, but the shoulders remain in their
place after rotation.
o After extension, the head comes out and becomes free, so it restitutes
in the opposite direction of internal rotation, so that the fetus becomes
coordinated with the shoulders (undo twist of internal rotation).

28. Delevery of the head
7. external rotation of the head and internal rotation of the shoulders:
- The shoulders undergo internal rotation in the same mechanism of internal
rotation of the head.
- The anterior shoulder is the one which enters the pelvis first. It descends
until it reaches the pelvic floor
-- Internal rotation of the shoulders leads to external rotation of the head.
In other words, external rotation of the head is explained by internal
rotation of the
shoulder

30. Delevery of the shoulders and trunk
-Anterior shoulder hinges below the SP
-The posterior shoulders is delivered first by lateral flexion of the
trunk
- The anterior shoulder then follow then the rest of the body

32. Third stage of labor
Starts by complete delivery of the fetus and ends by expulsion of placenta and membranes
Duration: 10 - 30 m in both primi-and multipara
Mechanism of separation of the placenta:
- After fetal delivery the uterus becomes smaller and
retractions continues so the placental site diminishes,
meanwhile the inelastic placenta is unable to shrink
- Bearing down help in expulsion of the already formed
placenta.

33. Mode of placental
separation
Duncan's mechanismSchultz's mechanism
Presented by maternal and fetal surfacePresented by fetal surface
The placenta separates from the lower
pole. When the blood vessels are cut,
bleeding occurs directly without
hematoma (clotting).
Placental separation is slower, so more
blood is lost.
Placental separation
Placenta separates from the center. So,
When the blood vessels are cut, some
bleeding occurs, forming a retro-placental
hematoma, facilitating the separation of
the placenta, making it quicker, and
therefore decreasing the bleeding.
Placental separation is slower because
there is no hematoma.
Placental separation is faster (because
hematoma makes separation faster)
more bleeding because placental
separation is slow
Less bleeding because placental separation is
faster.

34. Signs of placental separation
1- uterus becomes smaller and harder
2- supra pubic plug ( placenta in the LUS )
3- increase in length of cord outside of the vulva
4- failure of cord to recede when the uterus is
elevated by hand per abdomen
5- loss of impulse on the cord when pressure is
done on the fundus
6- gush of blood per vagina
7- lower pole of placenta is seen