Labor - Creighton University School of Medicine
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Transcript Labor - Creighton University School of Medicine
Labor
District 1 ACOG Medical Student
Education Module 2008
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
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 P’s:
Powers
Passenger
Passage
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.
Power
There is no specific criteria for adequate
uterine activity
Generally 3-5 contractions in a 10 minute
period is considered adequate labor
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
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not accurate and thus has been replaced by a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
Passage
www.uptodate.com
Passage - Pelvimetry
www.uptodate.com
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, 11.2 cm /hour, regular uterine contractions
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.
Labor
Freidman’s
curve is a good
guideline for
expected
progression in
labor and
therefore
helpful to note
abnormal labor
patterns.
Labor
NulliG
MultiG
1st Stage
Active
phase
Duration
6-18 h
2-10 h
Dilation
~1 cm/h
~1.5 cm/h
Arrested
>2 h
>2h
2nd Stage
0.5-3 h
5-30 min
3rd Stage
0-30 min
0-30 min
Labor
Variables associated with longer labors:
Electronic fetal monitoring
Narcotic use
Maternal age >30
Ambulation
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.
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
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
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
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
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
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.
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
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
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
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
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
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.
Cardinal Movements of Labor
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…