Fetal Orientation

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Fetal Orientation

Mechanism of Labor
Ob Gy Department, First Hospital, Xian Jiao
Tong University SHU WANG
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Fetal Orientation

• Fetal lie
• Fetal presentation
• Fetal position

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Fetal lie

• Refers to the relationship of the long axis of
  the fetus to the long axis of the mother
• Longitudinal 99 of all fetuses assume this lie.
• Transverse long axis of the fetus is
  perpendicular to the long axis of the mother.
• Result of over-relaxation of maternal abdominal
  wall
• Increased risk with multiple pregnancies
• Requires a C-section
• Oblique the relationship of the spines forms lt45
  degree angle.

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Fetal lie
Oblique
Longitudinal
Transverse
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Fetal presentation

• Presenting part
• Refers to the part of the fetus that enters the
  canal first
• Cephalic
• Vertex head with chin flexed toward chest (most
  common cephalic position)
• Face fetuss neck is hyperextended bringing the
  back of its head
• Breech 3 presentations
• Shoulder
• Compound

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Cephalic presentation
Vertex presentation
face presentation
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Breech presentation

• Frank breech (50-70) - Hips flexed, knees
  extended (pike position)
• Complete breech (5-10) - Hips flexed, knees
  flexed (cannonball)
• Footling or incomplete (10-30) - One or both
  hips extended, foot presenting

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Shoulder presentation
Compound presentation
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Normal presentation
Abnormal presentations
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Fetal position

• Determines the relationship of a designated point
  of the presenting part in relation to the
  maternal pelvis

Presentation Point of reference
Vertex Occiput
Face Chin (Mentum)
Breech Sacrum
Shoulder Scapula

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Fetal position

• Designated points used for the maternal pelvis
  follow

Left Occipital Anterior
Right Occipital Anterior
Anterior
Right
Left
posterior
Right Occipital Posterior
Left Occipital Posterior

• LOA fetal head is presenting with occiput
  directed toward the left side and anterior pelvis
  of the woman

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Occiput position
Left
Transverse
Right
Left Occiput Anterior LOP
Left Occiput Transverse LOT
Left Occiput Posterior LOP
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Mentum position
Left Mentum Anterior LMA
Left Mentum Posterior LMP
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Mechanism of Labor
The sequencing of events related to
posturing and positioning that allows the baby to
find the "easiest way out."
Mechanism of labor a series of passive, adaptive
movements of the fetal head and shoulders
smallest diameter to pass through the birth canal
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Review Pelvis
A-P d 11cm
Oblique d.12.75cm
Transverse d13cm
midpelvis
A-P d
A-P d.11.5cm
Transverse d.9cm
Transverse d10cm
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Review Axis of Pelvis
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Review Fetal cranium
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Review Fetal cranium
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Fetus makes his head smaller
flexion
gt
Occipitofrontal diameter
Suboccipitobregmatic diameter
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Mechanism of Labor

• Positional movements the fetus undergoes to
  accommodate itself through the maternal pelvis

Engagement Descent Flexion Internal rotation
Birth of the shoulders External
rotation Restitution Extension
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Engagement
Occurs when the fetal presenting part has passed
through the maternal inlet of the pelvis
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Descent
continuous downward movement of fetus through
birth canal
1. pressure by the amniotic fluid 2. direct
pressure by the contracting fundus on the
fetus 3. force of the contraction of the maternal
diaphragm and abdominal muscles in second stage
labor 4. extension and straightening of the fetal
body
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Flexion
shape of the uterus causes fetal neck to flex and
the chin rests on its chest

• Allows the smallest diameter of the head to
  pass through the smallest portion of the maternal
  inlet

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Internal rotation

• Allows fetal head to pass beneath the pelvic arch

rotation from a diagonal or transverse position
to an anteroposterior position
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Extension

• Fetal head extends to allow the birth of the
  occiput, face, and chin
• Occurs in response to the pressure from uterine
  contractions and shape of pelvic floor

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Restitution and external rotation

• After head is delivered, it immediately rotates
  to the left or right
• Assumes previous position that it was in during
  engagement
• Anterior shoulder is delivered first followed by
  the posterior shoulder

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Expulsion
Once shoulders are delivered, rest of the body
just slides out
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Critical Movements of labor
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• No two pelvis are exactly the same, just
  as no two faces are the same. For each pelvis
  there is an optimum mechanism that may be wholly
  different from the so-called normal mechanism.
  
  -------Caldwell and Maloy

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The end!
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Picture

• These children wish they could go home to a nice
  family but they have no home to go to everyday
  is a misery.

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Fantasies Can Come True

• Lets make these childrens fantasies a reality.