Labor

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Labor

• District 1 ACOG Medical Student Education Module
  2008

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Labor

• Labor is the physiologic process by which a fetus
  is expelled form the uterus to the outside world.
• It involves the sequential integrated changes in
  the uterine decidua, and myometrium.
• Changes in the uterine cervix tend to precede
  uterine contractions

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Labor - Mechanics

• Uterine contractions have two major goals
• To dilate cervix
• To push the fetus through the birth canal
• Success will depend on the three Ps
• Powers
• Passenger
• Passage

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Power

• Uterine contractions
• Power refers to the force generated by the
  contraction of the uterine myometrium
• Activity can be assessed by the simple
  observation by the mother, palpation of the
  fundus, or external tocodynamometry.
• Contraction force can also be measured by direct
  measurement of intrauterine pressure using
  internal manometry or pressure transducers.

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Power

• There is no specific criteria for adequate
  uterine activity
• Generally 3-5 contractions in a 10 minute period
  is considered adequate labor

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Passenger

• Passenger fetus
• Fetal variables that can affect labor
• Fetal size
• Fetal Lie longitudinal, transverse or oblique
• Fetal presentation vertex, breech, shoulder,
  compound (vertex and hand), and funic (umbilical
  cord).
• Attitude degree of flexion or extension of the
  fetal head
• Position
• Station degree of descent of the presenting
  part of the fetus, measured in centimeters from
  the ischial spines
• Number of fetuses
• Presence of fetal anomalies hydrocephalus,
  sacrococcygeal teratoma

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Passage

• Passage Pelvis
• Consists of the bony pelvis and soft tissues of
  the birth canal (cervix, pelvic floor
  musculature)
• Small pelvic outlet can result in cephalopelvic
  disproportion
• Bony pelvis can be measured by pelvimetry but it
  not accurate and thus has been replaced by a
  clinical trial of labor

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Passage

• www.uptodate.com

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Passage - Pelvimetry

• www.uptodate.com

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The Stages of Labor

• First Stage
• Interval between the onset of labor and full
  cervical dilation
• Two phases
• Latent phase onset o f labor with slow cervical
  dilation to 4 cm and variable duration
• Active phase faster rate of cervical change,
  1-1.2 cm /hour, regular uterine contractions

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The Labor Curve

• First stage - A latent phase B C D active
  phase B acceleration C maximum slope of
  dilation D deceleration E second
  stage.Adapted from Friedman. Labor Clinical
  evaluation and management, 2nd ed, Appleton, New
  York 1978.

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Labor

• Freidmans curve is a good guideline for expected
  progression in labor and therefore helpful to
  note abnormal labor patterns.

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Labor

• Variables associated with longer labors
• Electronic fetal monitoring
• Narcotic use
• Maternal age gt30
• Ambulation

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Labor Second Stage

• Interval between full cervical dilation to
  delivery of the infant.
• Characterized by descent of the presenting part
  through the maternal pelvis and expulsion of the
  fetus.
• Indications of second stage
• Increased maternal show
• Pelvic/rectal pressure
• Mother has active role of pushing to aid in fetal
  descent.

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Labor Second Stage

• Examining the fetal head during the second stage
  may become difficult due to molding
• Molding is the alteration of the fetal cranial
  bones to each other as a result of compressive
  forces of the maternal bony pelvis.
• Caput is the localized edematous area on the
  fetal scalp caused by pressure on the scalp by
  the cervix.
• PrimiG 0.5-3 h mulitG 0-30min

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Labor Third Stage

• The time from fetal delivery to delivery of the
  placenta
• Three signs of placental separation
• Lengthening of umbilical cord
• Gush of blood
• Fundus becomes globular and more anteverted
  against abdominal hand

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Labor Third Stage

• Placenta is delivered using one hand on umbilical
  cord with gentle downward traction. Other hand on
  abdomen supporting the uterine fundus.
• Risk factor for aggressive traction is uterine
  inversion.
• Obstetrical emergency!!
• Normal duration between 0-30 min for both PrimiG
  and MultiG

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Labor Fourth Stage

• Refers to the time from delivery of the placenta
  to 1 hour immediately postpartum
• Blood pressure, uterine blood loss and pulse rate
  must be monitor closely 15 minutes
• High risk for postpartum hemorrhage from
• Uterine atony, retained placental fragments,
  unrepaired lacerations of vagina, cervix or
  perineum.
• Occult bleeding may occur vaginal hematoma
• Be suspicious with increased heart rat, pelvic
  pain or decreased BP

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Cardinal Movements of Labor

• Refers to changes in the fetal head position
  during its passage through the canal.
• Seven distinct movements
• Engagement
• Descent
• Flexion
• Internal rotation
• Extension
• External rotation/restitution
• Expulsion

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Cardinal Movements of Labor

• Engagement
• Passage of the widest diameter fetal presenting
  part below the plane of the pelvic inlet
• The head is said to be engaged if the leading
  edge is at the level of the ishial spines.

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Cardinal Movements of Labor

• Descent
• Refers to the downward passage of the presenting
  part through the bony pelvis
• Not steady process
• Greatest at deceleration phase of first stage and
  during 2nd stage of labor

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Cardinal Movements of Labor

• Flexion
• Occurs passively as the head descends due to the
  shape of the bony pelvis.
• Partial flexion occurs naturally but complete
  flexion usually occurs only in the labor process
• Complete flexion places the fetal head in optimal
  smallest diameter to fit through the pelvis

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Cardinal Movements of Labor

• Internal Rotation
• Rotation of the fetal head from occiput
  transverse to occiput either in anterior or
  posterior position
• Occurs passively due to the shape of the bony
  pelvis

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Cardinal Movements of Labor

• Extension
• Occurs when the fetus has descended to the level
  of the vaginal introitus
• When occiput is just past the level of the
  symphysis, the angle of the birth canal changes
  to upward position

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Cardinal Movements of Labor

• External Rotation/Restitution
• As the head is delivered, it rotates back to its
  original position prior to internal rotation
• It aligns anatomically with the fetal torso
• The release of the passive forces on the fetal
  head allows it to return to appropriate position

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Cardinal Movements of Labor

• Expulsion
• Delivery of the fetus
• After delivery of the fetal head, descent and
  intraabdominal pressure by mother brings shoulder
  to the level of the symphysis
• Downward traction allows release of the shoulder
  and the fetus is delivered.

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Cardinal Movements of Labor
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In Summary

• Know the different stages of labor
• Know the labor curve
• Know the cardinal movements of labor
• Know the causes of postpartum hemorrhage
• The remaining talk regarding labor, induction,
  augmentation, surveillance and complications will
  be discussed in following lectures