Mechanism of Labor
                     MECHANISM OF LABOR
 The mechanism of labor covers the passive movement the 
fetus undergoes in order to negotiate through the maternal 
bony pelvis. Labor can be broken down into several key 
steps.
INTRODUCTION
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 Descent
 Engagement
 Neck flexion
 Internal rotation
KEY STAGES OF 
 Crowning
LABOR
 Extension of the presenting part
 Restitution
 External rotation
 Lateral flexion
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Descent is encouraged by:
 Increased abdominal muscle tone
 Braxton hicks in the late stages of pregnancy
 Fundal dominance of the uterine contractions during labour
 Increased frequency and strength of contractions during 
labour
DESCENT
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The term engagement is referring to the widest part of the 
fetal head successfully negotiating its way down deep into the 
maternal pelvis. Engagement is identified by abdominal 
palpation, where the fetal head is 3/5th palpable or less.
ENGAGEMENT
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As the fetus descends through the pelvis, fundal dominance of 
uterine contraction exerts pressure down the fetal spine 
towards the occiput, forcing the occiput to come into contact 
with the pelvic floor. 
FLEXION 
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The pelvic floor has a gutter shape with a forward and 
downward slope, encouraging the fetal head to rotate from the 
left or right occipito-transverse position a total of 90-degrees, 
to an occipital-anterior (occiput facing forward) position, to lie 
under the subpubic arch.
INTERNAL 
ROTATION
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When the widest diameter of the fetal head successfully 
negotiates through the narrowest part of the maternal bony 
pelvis, the fetal head is considered to be ‘crowning’. 
CROWNING
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The occiput slips beneath the suprapubic arch allowing the 
head to extend. The fetal head is now born and will be facing 
the maternal back with its occiput anterior.
EXTENSION
Source: geekymedics.com
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