Definition of labor
Physiology of labor
Mechanism of labor
Management of labor
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Labor is the physiological process by which a
fetus is expelled from the uterus to the outside
Labor is a clinical diagnosis, classically defined by
the triad of:
1 regular painful uterine contractions,
2 progressive cervical effacement
3 show (bloody discharge).
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Diagnosis of labor
- At least two contraction per 20 minutes lasting 20
- Cervical dilatation of 3-4 cm or more
- Cervical effacement of 80% or more
- Rupture of membranes
At least two criterias needed to make the
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1) Show should be disregarded if there is a
membrane rupture or digital PV exam done
with in 48 hours prior to show.
2) Rupture of the membranes without presence
of painful uterine contractions is PROM,
3) Cervical change without presence of painful
uterine contractions is either cervical
incompetence, or a normal finding in most
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WHO definition of normal labor and
spontaneous in onset & at term
low-risk at the start of labor and remaining so
throughout labor and delivery.
The infant is born spontaneously
in the vertex position & single ton
After birth, mother and infant are in good
within a reasonable time (not less than 3 hours or
more than 18 hours)
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Physiology of labor
• The physiology of labor initiation has not
been completely elucidated.
• Labor is species specific, mechanism in
humans is unique.
1. Hormonal factors:
a. Estrogen theory: During pregnancy, most
estrogens are in binding state.
• more free estrogen appears increasing the
excitability of the myometrium and
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b. Progesterone withdrawal theory
c. Prostaglandins theory: PGF2a was found to be increased
in maternal and fetal blood as well as the amniotic fluid
late in pregnancy and during labor.
d. Oxytocin theory: The secretion of oxytocinase enzyme
from the placenta is decreased near term due to
placental ischemia leading to predominance of oxytocin’s
e. Fetal cortisol theory: Increased cortisol production by
adrenal increases estrogen production.
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2. Mechanical factors:
a. Uterine distension theory: explains the
preterm labor in case of multiple pregnancy
b. Stretch of the lower uterine segment by the
presenting part at term
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Phases of labor
• Phase 0 (Phase of quiescence):
- Refers the time in utero before onset of labor.
- Uterine activity is suppressed
• Phase 1 (Activation phase):
- Estrogen facilitates expression of myometrial
receptors for PGs and oxytocin- Gap junctions
- Prepares the uterus for subsequent stimulation
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• Phase 2 (Stimulation phase):
- Uterotonics, particularly PGs and oxytocin stimulate
regular uterine contractions
• Phase 3 (Uterine involution):
- After delivery, mainly mediated by oxytocin.
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Mechanisms of labor
• It is also known as the cardinal movements,
described in relation to a vertex presentation
• cardinal movement refers to the changes in position
of fetal head during its passage through the birth
• Because of asymmetry in fetal head and maternal
pelvis, such rotations are needed for negotiation.
• Although labor and delivery occurs in a continuous
fashion, the cardinal movements are described as 7
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Cardinal movements - cont’d
1. Engagement: the passage of widest diameter of
presenting part to a level below the plane of pelvic
inlet. On the pelvic examination, the presenting
part is at 0 station, or at the level of the maternal
2. Descent: downward passage of presenting part
through the birth canal
- This occurs intermittently with contractions.
- Greatest descent occurs in deceleration phase (late
active stage) & second stage
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3. Flexion: Occurs passively
- Helps to present the smallest presenting diameter (i.e.
from occipitofrontal (11.0 cm) to suboccipitobregmatic
(9.5 cm) for optimal passage through the pelvis.).
4. Internal rotation: Passive movement due to shape of
pelvis and pelvic musculature.
- Rotation of the presenting part from its original position
to AP position & in line with the AP diameter of the
5. Extension: Occurs once fetus descended to a level of
- Is because of force of uterine contraction versus muscles
of the pelvic floor. the result is delivery of the head
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6. External rotation: also called as restitution
- Return of fetal head to the correct postion in
relation to fetal torso.
- Passive movement
- Results from maternal bony pelvis & its
musculature and basal tone of fetal
7. Expulsion: Delivery of rest of fetus.
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STAGES OF LABOR
• Four arbitrary stages of labor: to facilitate study and to
assist in clinical management.
- First stage of labor: onset of labor till full(10cm)
Latent phase: onset of labor to 3 cm cervical
Active phase: 4 cm – 10 cm cervical dilatation.
• Rate of cervical dilatation is 1.2cm/hr in primi & 1.5
cm/hr for multi
• Average duration of first stage is 12 hrs in primi and 6
hrs in multi.
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from full cervical dilatation of cervix to
delivery of fetus.
Second stage lasts an hour in primi and 20
minutes in multi.
Rate of descent is 1cm/ hr in primi & 2cm/hr
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• Third stage of labor: from delivery of fetus till
delivery of placenta.
• Average duration is 15 minutes for both.
• FOURTH STAGE: first one to two hours after
delivery of placenta, where PPH is high.
- This stage is a critical time for monitoring of
vital signs and observe for blood loss &
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Success of labor determined by 3P’S
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Labor - Mechanics
1 Powers (uterine contractions)
It has two major goals:
• To dilate cervix
• To push the fetus through the birth canal
- Simple observation
- Manual palpation
- External objective assessment-tocodynamometer
- Direct measurement by intrauterine pressure
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• Adequate uterine contraction
3-5 contractions in a 10 minute period
???Hyper stimulation, tachysystole, hypertonus.
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2 Passenger (fetus)
1. Fetal size
2. Fetal Lie – longitudinal, transverse or oblique
3. Fetal presentation – vertex, breech, shoulder,
4. Attitude – degree of flexion or extension of the fetal
5. Position _ Depending on the reference point or
6. Station – degree of descent of the presenting part of
the fetus, measured in centimeters from the ischial
7. Number of fetuses
8. Presence of fetal anomalies – hydrocephalus,
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3 Passage (pelvis)
• Consists of the bony pelvis and soft tissues of
the birth canal.
• Bony pelvis can be measured by pelvimetry
but it is not accurate and it has been replaced
by a clinical trial of labor.
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True labor Vs False labor
True labor pain False labor pain
Increase progressively not
Lower abdomen & back Lower abdomen
Dilatation & effacement of
No effect on cervix
Not relieved by sedatives
MANAGEMENT OF NORMAL LABOR
Admission criteria for labor
1. All women with diagnosis of labor ( latent and
active) with ruptured membranes, or
2. All women with diagnosis of labor ( latent and
active) with known risk factor, or
3. All women with diagnosis of active labor (i.e.
cervix dilation is ≥ 4 cms with complete or 100%
effacement) with/without presence of rupture of
membranes or risk factor
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MANAGEMENT OF NORMAL LABOR(ctd)
• Psychosocial issues
- emotional support
- Inform about maternal & fetal conditions
- Review prenatal record for medical &
- check development of new disorder
- Thorough history & physical examination
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MANAGEMENT OF NORMAL LABOR(ctd)
• Laboratory Studies
BG &Rh ,Hct /Hgb ,HIV test, Urine analysis
• Position: can assume any position except
• Diet: fluid diet, intravenous hydration when
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Management of the First Stage of Labor
FHB every 30 minutes in low risk & every 15
minutes in high risk
- FHB has to be counted for a full minute just
- Uterine contraction every 30 minutes, monitor
for 10 minutes
- Pelvic evaluation every 4 hrs unless indicated.
- Maternal vital signs: every 2-4 Hrs
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Management of the Second Stage of Labor
-FHB every 15 minutes in low risk & 5 minutes
in high risk mothers.
- Monitor descent hourly.
- Expulsive Efforts:instruct to exert downward
pressure as though she were straining at stool during
- DELIVERY: use aseptic technique
Reduce risk of maternal perineal injury
Prevent fetal injury
Provide initial support to newborn
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Active management of the third Stage
• use of utertonics,
• controlled cord traction and
• uterine massage
Who should get AMTSL?
What are benefits of AMTSL?
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• It is the graphic recording of the progress of
labor and the salient condition of the mother
• Designed by WHO for use in developing
• It serves as an “early warning system” .
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- Patient information
- Fetal condition
- Progress of labor
- Maternal condition
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Advantages of partograph
• Early detection of abnormal labor and
prevention of prolonged labor
• ↓ maternal - perinatal morbidity & mortality
• Pictorial (graphic or clear) display of events of
- Clarifies recordings
- Avoids lengthy written notes
- Facilitates recognition of any omissions
- Saves time → Companionship
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Advantages of partograph(ctd)
• Low cost, feasible
• All interrelated variables of labor can be
seen on a single paper.
• Hand over of patients
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Quiz on Review of labor
1 What is labor?
2 What are the diagnostic criteria of labor?
3 List down criterias for of normal labor.
4 What are determinant factors for success labor?
5 What are the admision criterias of labor?
6 List down cardinal movements in their order.
7 Who should get AMTSL?
8 What are benefits of AMTSL?
9 How do differentiat true from false labor?
10 List down component & advantages of partograph.
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