This document provides an outline on normal labor and the mechanism of labor. It defines labor as the physiological process of expelling the fetus, placenta, and membranes through the birth canal after 24 weeks of pregnancy. Normal labor fulfills criteria of spontaneous onset at term, vertex presentation, no prolongation, and natural termination with minimal aids. The document describes the three stages of labor as well as the cervical changes, fetal positioning, and mechanisms involved in labor including engagement, descent, flexion, rotations, and expulsion of the fetus through the birth canal. It emphasizes the importance of classifying pregnancies as high or low risk and addressing any medical issues to ensure a safe delivery.

1. NORMAL LABOUR
&
MECHANISM OF LABOR
PROFESSOR DR. IRAM CHAUDHRY
FCPS(OBS&GYNAE), MHPE

2. OUTLINE
• Definition of Labor
• Mechanism of Labor
• Stages of Labor
• Management of Normal
Labor

3. Labour
• It is a physiological process by which the
fetus, placenta and membrane are expelled
out through the birth canal after twenty four
week of pregnancy
• Parturition isthe process of givingbirth

4. Normal labour
• Normal labour is physiological process by
which the fetus ,placenta and membrane are
expelled through the birth canal after full
term pregnancy (37-42 weeks ofgestation)

5. • Labour is called normal when it fulfills
the following criteria :
 Spontaneous onset at term
 With vertex presentation
 Without prolongation
 Natural termination with minimal
aids

6. Clinical course of labour
Onset of labour: not definitely known
Mechanical factors:
- uterine distension
Hormonal factors:
1. Maternal :
o progesterone withdrawal
o oxytocin stimulation
o prostaglandins
o serotonin
2. fetal:
o fetal cortisol
o fetal membranes
3. Neuronal:
o sympathetic- alpha receptor stimulation

7. 1- Regular Uterine Contractions
2- Show
3- Leaking

8. NORMAL LABOUR
FIRST STAGE
SECOND STAGE
THIRD STAGE
LATENT PHASE: 0-6cm
ACTIVE PHASE: 6-10cm
FULL DILATION TO EXPULSION OF FETUS
BIRTH TO EXPULSION OF PLACENTA
Expectant (physiological) vs Active (CCT + OT)

9. 1. True labour pains – colicky pain in the abdomen and back
are characterized by:
A Character True l.pains False l.pains
Irregular
Short duration, not
progressive
contractions
Interval between
contractions and
intensity
Changes in the cervix
Membranes
Response to analgesia
Labour
regular
Progressive (increase in
frequency and
intensity)
Associated with
effacement and dilation
of the cervix
Associated with bulging of
membranes
Not relieved by sedation
Followed by labour
Not associated with
effacement and dilation
of the cervix
Not associated with
bulging of membranes
Relieved by sedation
Not followed by labour

10. • Cervicaldilatation:
• Thecervix begins dilating and stretching
beyond the normal dimensions and is
measured in centimeters. (0-10cm).
• Cervicaleffacement:
• softening, thinning and shortening of the
cervix. It is expressedin percentage (0 –
100%)

11. Cervical effacement
vs
cervical dilation
Cervix closed,
3 cm long
Cervix effaced,
1 cm dilated
Cervix
5 cm dilated
Cervix
fully dilated

12. Factors affecting Labor (5 P’s)
In every labor; there are five essential factors affect the
process. 5 P’s:
1. Passenger: the fetus
2. Passageway: the pelvis and birth canal
3. Powers: the uterine contractions
physical
4. Position: maternal postures and
positions
5. Psyche: the response of the mother
7

13. 1.Passenger (The Fetus):
The fetus relationship to the passageway is the major
factor in the birthing process. The relationship includes:
• Fetal skull and size
• Number of fetuses
• Position of feus
– Fetal lie: relationship of fetal spine to maternal spine;
longitudinal (vertical) or transverse (horizontal)
– Fetal presentation: part of fetus that enters pelvis first
– Fetal attitude: relationship of fetal body parts to each other;
flexion (normal) or extension (abnormal)
– Fetal position: fetal direction in the pelvis
– Fetal station: position of the baby's head relative to the lower
bone of pelvis called the ischial spines 8

14. Fetal Lie & Presentation

17. Fetal Attitude 10
Complete extension
(abnormal)
Complete flexion
(normal)

18. Fetal Position
11

19. 2. Passageway (The pelvis):
• Includes bony pelvis, soft tissues of the cervix,
and vagina.
• The maternal pelvis is the greatest determinant
in the vaginal delivery of the fetus.
• During the first stage of labor, the cervix dilates
and thins out (effaces).
• The cervix must be 100 percent effaced and 10
centimeters dilated before a vaginal delivery.

20. Fetal Station 12

21. 14

22. ST
AGESOFLABOUR:
First stage:
stageof cervical effacement and dilatation
Definition:
refers to the period from the onset of true
uterine contractions to full dilation of cervix,
when it measures 10cm.

23. 15

24. 29

25. Secondstage of labour:
stage of delivery of the fetus.
Definition:
the second stage refers to the period from complete
cervical dilatation to the birth of thefetus.
Duration:
primigravida =2h
multigravida =1h
However the duration of second stage is
controversial

26. 31

27. Third stage of labour:
The stage of expulsion of placenta and
membranes.
Duration:
upto30minutes,averagetimeis10 minutes

28. 33

29. 34
clamp and cut of the umbilical cord

30. Stageof
labour
Definition Duration
StageI latent
phase
(affacment)
•Beginsfrom the onset of regularcontractions.
•Endswith acceleration of cervicaldilatation
•Prepares cervix for dilatation.
<20hours in PG
<14hours MG
Stage1 active
phase
(dilatation)
•Beginswith acceleration of cervicaldilatation.
•Endsat 10 cmdilatation
•Rapid cervical dilatation
<2/hours in PG
<1.5/ hrs inMG
Stage2
(descent)
•Beginsfrom 10cmdilatation
•Endswith delivery of thebaby
•Descent of the fetus
<2hours in PG
<1hours in MG
Add 1 hour inepi
Stage3
(expulsion)
•Beginswith delivery of thebaby.
•Endswith delivery of theplacenta
•Delivery of the placenta
<30min.

31. Mechanism of Labor
19
In the normal labor; there are series of changes in position
and attitude of the fetus to accommodate himself to the
pelvic to pass easily through the birth canal:
1. Engagement
2. Descent
3. Flexion
4. Internal rotation
5. Extension
6. External rotation
7. Expulsion

32. 1. Engagement
20
of the fetal head passes
The greatest diameter
through the pelvic inlet.
2. Descent
Movement of the fetus through the birth canal
during the first and second stages of labor
3. Flexion
The chin of the fetus moves toward the fetal chest
which reduce the fetal head diameter from nearly 12
to 9.5 cm.

33. 21

34. 4. Internal rotation
The rotation of the fetal head until the longest
diameter of the fetal head match the longest
diameter of the maternal pelvic.
22

35. 5. Extension
The fetal head passes beneath the symphysis
pubis and passes out of the birth canal making the
crowning.
23

36. 6. External rotation (Restitution)
After the head has delivered, the shoulders
rotate internally to fit the pelvis.
24

37. 7. Expulsion
The shoulders and remainder of the body are
delivered
25

38. During antenatal period, the women should be
classified as high or low risk pregnancy.
The medical or surgical problems should be corrected
(anaemia, hypertension, urinary tract infection),
Vaccination
Investigations
(HIV, HCV, Hbs Ag, blood grouping).
Advise her to attend atenatal classes and hospital
delivery.

39. Thank you