Ch. 11. Parturition

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Ch. 11. Parturition
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Clinical Course of Labor
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INDEX
1. The Myometrium
2. The Cervix
3. Labor Patterns
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Labor thunderous uterine contractions that
effect dilatation of the cervix and
force the fetus through the birth
canal False labor myometrial contractions
that do not cause cervical
dilatation unpredictability in
occurrence lack of intensity
brevity of duration discomfort
confined to low abdomen groin
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The Myometrium
1. Anatomical and Physiological Considerations
Characteristics advantage in the
efficiency of uterine
contractions the delivery of the fetus
? degree of shortening of smooth muscle cells
with contraction magnitude
greater than in striated muscle cells ?
forces can be exerted in smooth muscle cells in
any direction ? not organized in
the same manner as skeletal muscle -
thick thin filaments in long, random bundles
? greater shortening
force-generating capacity ?
multidirectional force generation
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The Myometrium
2. Biochemistry of Smooth Muscle Contractions
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The Myometrium
3. The Three Stages of Labor First stage of
labor begins when uterine
contraction of sufficient frequency,
intensity duration are attained ?
ends when cervix is fully dilatated (10cm)
stage of cervical effacement dilatation
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The Myometrium
Second stage of labor begins when
complete dilatation of cervix ? ends
with delivery of the fetus stage of
expulsion of the fetus Third stage of
labor begins after delivery of the fetus
? ends with the delivery of the
placenta stage of separation expulsion
of placenta
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The Myometrium
4. Clinical Onset of Labor Show (bloody
show) - sign of the impending onset
of active labor - extrusion of mucus plug
of the cervical canal ? discharge of
small amount of blood-tinged mucus
from vagina
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The Myometrium
5. Uterine Contractions Characteristic of Labor
muscular contractions, those of uterine
smooth muscle of labor are painful
cause of pain (not known definitely) ?
hypoxia of contracted myometrium ?
compression of nerve ganglia in cervix lower
uterus by the tightly interlocking muscle
bundles ? stretching of cervix during
dilatation ? stretching of peritoneum
overlying the fundus
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The Myometrium
Ferguson reflex mechanical
stretching of cervix enhances uterine
activity manipulation of the cervix and
stripping the fetal membranes is
associated with an increase in PGF2a
metabolite in blood exact mechanism not
clear Interval between contractions
10 minutes at the onset of the first stage
? diminishes gradually ? 1 minute
or less in the second stage
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The Myometrium
Periods of relaxation between contractions
- essential to welfare of the fetus
- unremitting contraction of uterus compromises
uteroplacental blood flow, cause fetal
hypoxia Duration of contraction
in active phase Duration 30-90
seconds (average 60 sec) Pressure
20-60 mmHg (average 40 mmHg)
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The Myometrium
6. Differentiation of Uterine Activity
During active labor, uterus is transformed into
2 distinct parts (1) Upper segment
? actively contracting ? becomes
thicker as labor advances ? quite firm
or hard (2) Lower segment ?
relatively passive ? develops into a
much thinly walled passage for the
fetus ? much less firm
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The Myometrium
Physiologic retraction ring - As a
result of the thinning of the lower uterine
segment and the concomitant thickening of the
upper, the boundary between the two is
marked by a ridge on the inner uterine
surface Pathologic retraction ring (the
ring of Bandle) - When the thinning of the
lower uterine segment is extreme, as in
obstructed labor, the ring is very
prominent
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The Myometrium
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The Myometrium
7. Change in Uterine Shape each contraction
produces elongation of uterus with decrease
in horizontal diameter ? important effect
on labor process ? decrease in horizontal
diameter ? straightening of fetal
vertebral column ? lengthening of uterus
? longitudinal fibers are drawn taut ?
pulled upward the lower segment cervix
? important factor in cervical dilatation
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The Myometrium
8. Ancillary Forces in Labor After the
cervix is dilated fully, the most important
force in the expulsion of the fetus is that
produced by increased maternal intrabdominal
pressure Pushing - increased
intrabdominal pressure by contraction of
abdominal muscles, simultaneously with forced
respiratory efforts with glottis closed
- important force in the expulsion of fetus
- similar to that involved in defecation
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The Cervix
1. Changes Induced in the Cervix with Labor
Effective force of the 1st stage of labor is
uterine contraction As the result of
the action of these forces, two fundamental
changes take place in the already ripened
cervix effacement dilatation The
cervix is said to be completely (fully)
dilated 10 cm
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The Cervix
2. Cervical Effacement obliteration or
taking up of the cervix shortening of the
cervical canal (2cm ? mere circular
orifice with almost paper thin edge)
muscular fibers at about the level of the
internal os are pulled upward or taken up
into the lower uterine segment external
os remains temporarily unchanged
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The Cervix
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The Cervix
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The Cervix
3. Cervical Dilatation as the uterine
contraction cause pressure on the membranes
? the hydrostatic action of the amnionic sac
in turn dilates the cervical canal
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Labor Patterns
1. Pattern of Cervical Dilatation
Friedman Except for cervical dilatation
fetal descent, none of the clinical
features of parturient appears to be
useful in assessing labor progression
pattern of cervical dilatation during normal
labor course sigmoid curve
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Labor Patterns
- 2 phases of cervical dilatation (1) Latent
phase more variable subject
to sensitive changes by extraneous factors
and by sedation (prolongation) and myometrial
stimulation (shortening) (2) Active
phase ? Acceleration phase
usually predictive of the outcome of a particular
labor ? Phase of maximum slope
good measure of the overall efficiency of the
machine ? Deceleration phase
more reflective fetopelvic relationship
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Labor Patterns
- 2nd stage of labor commences after complete
cervical dilatation? only progressive descent
of fetal presenting part is available to
assess the progress of labor
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Labor Patterns
2. Pattern of Descent - In many nulliparas,
? engagement is accomplished before labor
begins ? further descent does not occur
until late in labor ? increased rates of
descent are ordinarily observed
during the phase of maximum slope
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Labor Patterns
3. Criteria of Normal Labor Friedman
Concept of 3 functional divisions of labor
? Preparatory division - latent
acceleration phases - sensitive to
sedation conduction analgesia - little
cervical dilatation occurs, considerable
changes take place in the extracellular matrix
of cervix (collagen other connective
tissue component)
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Labor Patterns
? Dilatational division - phase of
maximum slope of cervical dilatation -
most rapid rate of dilatation occur -
unaffected by sedation or conduction analgesia
? Pelvic division - deceleration phase
second stage - involve the cardinal
movement of the fetus
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Labor Patterns
4. Rupture of the Fetal Membranes -
spontaneous rupture of membrane most often()
sometime during the course of active labor
- premature rupture of the membrane
rupture of membranes before the onset of labor
at any stage of gestation
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Labor Patterns
5. Placental Separation 3rd stage of
labor begins immediately after
delivery of the fetus, involve the
separation expulsion of the placenta
after delivery of placenta fetal membranes,
active labor is completed occurs
within a very few minutes after delivery
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Labor Patterns
6. Separation of Amniochorion great decrease
in the surface area of uterine cavity ?
fetal membranes (amniochorion) parietal
decidua to be thrown into innumerable folds
? increase thickness of the layer from less
than 1 mm to 3-4 mm
membranes usually remain in situ until placental
separation is nearly completed
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Labor Patterns
7. Placental Extrusion women in recumbent
position frequently cannot expel placenta
spontaneously ? artificial means of
completing the 3rd stage is generally
required ? compress elevate fundus
while exerting minimal traction on
umbilical cord
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Labor Patterns
8. Mechanisms of Placental Extrusion (1)
Schultze mechanism placental separation
occurs first at central areas ?
retroplacental hematoma ? push the
placenta toward uterine cavity (2) Duncan
mechanism ? placental separation occurs
first at the periphery ? blood collects
between the membranes uterine wall
? escapes from the vagina
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