Normal Labor or Delivery
Chen Danqing Women’s hospital,School of medicine,
Zhejiang University
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Objective
Definition of labor.
Determinate Factors of
Labor
Anatomical considerations:
 The female pelvis.
 The fetal skull.
The stages of labor.
The mechanism of labor
(vertex, LOA).
Management of normal labor.
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Definitions ： Labor
is the process by which
contractions of the gravid uterus expel the fetus and
the other products of conception after 28 weeks from
the last menstrual period.
It begins when uterine contractions of sufficient
intensity, frequency & duration are attained to bring
about progressive effacement & dilatation of the
cervix as well as descent of the presenting part.
Spontaneous or induced
Term or preterm
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Term Delivery：A term delivery occurs
between 37 and 42 weeks from the last
menstrual period.
Premature Delivery：Preterm labor is that
occurring before 37 weeks of gestational age.
Postdate pregnancy：Postdate pregnancy
occurs after 42 weeks .
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The etiology of labor
These mechanisms are not well defined in humans.
Cervix ripend and lower uterine segment development theory；
Endocrine regulating theory；
Mechanical theory；
Neurohumor theory ；
Immunologic theory；
Maturation of fetus and change of uterus function is necessary.
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Four Determinate Factors of Labor
The progress and final outcome of labor are
influenced by 4 factors .
(1)the powers
(2)the passage
(3)the passenger
(4)the psyche
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The Expulsive Forces(The powers)
The power that expulse the fetus
and the other products of
conception is called the expulsive
forces, which include
♀ Uterine contraction
♀ Intra-abdominal pressure
♀Levator
ani
muscles
contractions.
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Uterine Contractions
Have three unique characteristics:
★Rhythm: increase in frequency and duration,is the
important marker of in labor。rhythm
★ Symmetry
and polarity Symmetry and
polarity
★ Retraction Retraction
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Rhythm
Increase in frequency and duration
Periods of relaxation between contractions are essential to
the welfare of the fetus.
极期
进行
退行
宫缩
间歇期
宫缩
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Symmetry and Polarity
The intensity of the upper segment of
the uterus is the most strong
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The Intra-Abdominal Pressure
＆It is a necessary auxiliary to uterine contractions
in second stage of labor.
＆After the placenta has separated, its spontaneous
expulsion is aided by the mother increasing intraabdominal pressure.
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腹肌
子宫收缩力
膈肌
肛提肌
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Levator ani muscles contractions
※ Form a V-shaped sling that tends to rotate
the occipital anteriorly(internal rotation).
＆ Help the fetus’ extension and delivery.
＆Help the expulsion of the placenta.
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Passage
including: the bony pelvis and soft tissues
of pelvis
True vs. false
pelvis.
True pelvis:



Pelvic brim.
Pelvic cavity.
Pelvic outlet.
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bony pelvis
骶 骨
髂 骨
Os sacrum
os ilium
尾骨
Os coccyx
坐骨结节
Os ischium
骶尾关节
Sacro-iliac
jiont
耻骨联合
Symphysis publis
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The bony pelvis (the true pelvis)
Pelvic inlet plane
Pelvic midplane
Three pelvic plane:
Pelvic outlet plane
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The Pelvic Inlet
Shape:

Oval & in one plane.
Boundaries:



Anteriorly: SP.
Laterally: upper margin of pubic bone &
iliopectineal line.
Posteriorly: sacral promontory.
Dimensions:

AP=11 cm17
Transverse=13.5 cm.
The true conjugate
The inclined diameter
The transverse diameter
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Three anteroposterior diameters of
the pelvic inlet
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Pelvic Midplane
The smallest plane of the pelvis, particular
importance in obstructed labor.
Anteroposterior diameter of mid pelvis,average
11.5cm.
Transverse diameter of mid pelvis,alse be called
interspinous diameter,average 10cm.
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Anteroposterior diameter of
mid pelvis
Transverse diameter
of mid pelvis
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Transverse diameter of the midpelvis
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Pelvic Outlet Plane
Four diameters,
Anteroposterior, diameter of outlet, 11.5cm。
Transverse outlet, the distance between the inner
edges of the ischial tuberosities,9cm
Anterior sagittal diameter,6cm
Posterior sagittal diameter,8.5cm
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1、Transverse outlet
2、 Anterior sagittal
diameter
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3、 Posterior sagittal
diameter
4、 Anteroposterior
diameter of outlet
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Pelvic axis and Inclination of pelvic
Pelvic axis：The axis of the pelvis refers to the curve of the
birth canal as described by a line drawn through the
center of each of the four planes.
Inclination of pelvic :The angle of the pelvic inlet plane
with ground level when women stand.always 60 degree.
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pelvic axis
inclination of pelvic
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The Soft Part of the Birth Canal
Formation of lower uterine segment,cervix,
vagina,soft tissue in the floor of pelvis.
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The Lower uterine segment
Developed from the isthmus of the uterus of
nonpregnant women.
Physiologic retraction ring : The actively
contracting upper segment becomes thicker as
labor advances,the lower uterine segment is
relatively thin compared with the upper
segment,between them a physiologic retraction
ring appear.
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Changes of cervix
Effacement of cervix
The upper segment contracts, retracts, and expels the
fetus; in response to the force of the contractions of the
upper segment, the ripened lower uterine segment and
effacement of cervix.
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Dilatation of Cervix
In response to the
force of the
contractions of the
upper segment,
effacement of cervix
and dilatation,
through which the
fetus can be extruded.
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Change of cervix during labor
Effacement of cervix
dilatation of cervix
primigravida
multipara
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A crook canal formed by the vagina、tissue of
pelvic floor and perineum as the fetal descending.
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Passenger
Fetus(weight,position,presentation,
malformation)
Fetal weight, 2500g - <4000g
Fetal lie, the relation of the fetal long
axis to that of the mother.
Fetal presentation, the presenting
part is either foremost within the birth
canal or in closest proximity to it.LOA
LOP LOT ROA ROP ROT
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Size of the fetus head
Very important for delivery。
The vault is composed of 2 frontal bones,2 parietal
bones, 2 temporal bone and one occipital bone.
They are slightly separated from one another at the
margins of abutment and by wider spaces, the
anterior and posterior fontanelles.
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Four diameter of fetus head：
Biparietal diameter,The greatest transverse diameter of the
head,which extends from one parietal bone to other.
Average 9.3cm.
Occipito-frontal diameter：Which follows a line extending
from a point just above the root of the nose prominent portion
of the occipital bone. Average 11.3cm.
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Suboccipito-bregmatic diameter.
Which follows a line drawn from the middle of the large
fontanel to the undersurface of the occipital bone just
where it joins the neck. Average 9.5cm
Occipito-mental diameter：From the chin to the most
prominent portion of the occiput. Average 13.3cm
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Suboccipito-bregmatic
occipito-frontal
Occipito-mental diameter
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Position of the fetus
Fetal position of a particular presentation refers to the
relationship of an arbitrary reference point on the fetus
to a specific point in the right or left side of the maternal
pelvis.
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Psychologic Factors
A high level of anxiety during pregnancy
has been associated with decreased uterine
activity and with longer and dysfunctional
labor。
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Mechanism of Labor
Mechanism of normal labor in occiput presentation
include these cardinal movements of labor.
engagement
descent
flexion
internal rotation
Extension
external rotation,and expulsion.
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Engagement The mechanism by which the biparietal
diameter,the greatest transverse diameter of the fetal
head in occiput presentations,passes through the pelvic
inlet is defined engagement.
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Descent
Descent continues progressively until the fetus is
delivered;the other movements are superimposed
on it.
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Flexion
In flexion,the chin is brought
into more intimate contact
with the fetal thorax,and the
appreciably shorter
suboccipitobregmatic
diameter(9.5cm) is substituted
for the longer occipitofrontal
diameter(11.3cm).
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Internal rotation
Internal rotation is a turning of the fetus occiput
gradually moves from its original position
anteriorly toward the symphysis pubis about 45
degrees. It’s always finished in the end of the first
stage of labor.
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Extention
Extention brings the base of occiput into direct
contact with the inferior margin of the
symphysis pubis.
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Restitution
The fetus head rotates to the position it occupied at
engagement after it deliveried, following this the
shoulders descend in a path similar to that traced by the
head.
External rotation
The anterior shoulder rotates internally about 45 degrees
to come under the pubic arch for delivery.The head
continutly rotates left about 45 degrees to its position at
birth.
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Flowing these maneuvers, the body,legs,and feet are deliveried.
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Diagnosis of labor
Threatened labor
False labor:
1.
2.
3.
4.
5.
6.
Contractions occur at irregular intervals.
Intervals remain long.
Intensity remains unchanged.
Discomfort is chiefly in lower abdomen.
Cervix does not dilate.
Discomfort is usually relieved by sedation.
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Lightenting
The settling of the fetal head into the brim of the
pelvis.
Bloody Show
The mucus plug is expelled from the cervix mixing
with a little blood.
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In labor
Onset of labor is spontaneous uterine contraction with
progressive dilation of the cervix
uterine contraction
interval < 5 ’
lasting >30’’
intensity is middle or heavy
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Duration of Labor and Satges
The total stage of labor begins with the regular
uterine contractions and ends when delivery of the
placenta complete.
Normal labor is a continuous process which has
been divided into three stages for purposes of study.
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First stage of labor
The first stage begins with the onset of labor and ends
when dilation of cervix (10cm) is complete.
The average duration of the first stage of labor in a
primigravida is 11-12 hours;in a multipara 6-8 hours.
Clinical finding:
Rhythm contraction
Cervical dilation
Descend of presentation
Rupture of membranes
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Clinical course and treatment in first stage
Contraction
Dilation of cervix and decent of presentation
the latent phase ( onset to <3cm, <16h)
the active phase(>3cm to 10cm, <8h)
Rupture of membranes
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Management of the first stage:
⊙Blood pressure、 fetal heart rate 、cervical dilation、fetus
descending、uterine contraction；
⊙ When the membranes ruptured,please check the fetal heat
rate,fluid colour and amount at once
Fetal heart rate 120～160bpm
latent stage 1～2h fetal heat rate
active stage 15-30 minute
⊙ Need for subsequent vaginal examinations to identify the
status of the cervix and the station and position of presenting
part will vary considerably.
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Second stage of labor
The second stage of labor extends from full dilation of the
cervix to the birth of baby and varies from a few minutes to
about two hours depending on both fetal and maternal
factors.
primigravida <2h
multipara <1h
Third stage of labor
From the birth of the infant to delivery of the
5－15min, <30min
placenta
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Management of the second stage
■Fetal heart rate: should be measured at least
every 5～10min.
■ Maternal expulsive efforts.
■ Preparation for delivery
primigravida from cervical dilation completed
multipara from cervical dilation 4cm
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Management of third stage of labor.
Clinical course
After delivery of the infant,the height of the uterine
fundus and its consistency are ascertained.
Uterine contraction reappear after stopping for few
minutes.
Placental separation
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Signs of placental separation：
a.the uterus becomes globular and firmer.
b.The umbilical cord lengthened outside the vagina
c.A fresh show of blood from vagina
d.the uterus fundus rises up.
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Pay attention to:
Examine the placenta to ensure complete removal.
Examine the soft part of the birth canal.
Prevention of excessive postpartum bleeding.
Uterine contraction 、bladder distension
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