OB Exam #3 Intrapartum
1. Physiology of labor (for example: what happens when the uterus contracts)
a. Maternal effects
i. Reproductive system
1. Characteristics of contractions
a. Coordinated
i. Frequency: beginning of one uterine contraction to
the beginning of the next
ii. Duration: beginning of a uterine contraction to the
end of the same contraction
iii. Intensity: strength of a contraction (only tested
using an internal monitor)
b. Involuntary
i. Not under conscious control. The mother cannot
decide when to start or end the contraction
c. Intermittent
i. This allows for relaxation of the uterus and
resumption of blood flow back to the placenta
d. Interval
i. The period of time from the end of one contraction
to the beginning of the next
2. Contraction Cycle
a. Increment: period of increasing strength
b. Acme: The period during which the contraction is the most
intense
c. Decrement:The period of decreasing intensity as the uterus
relaxes
3. Uterine Muscle
a. The upper two thirds of the uterus contract actively to push
the fetus down, muscle wall becomes thicker
, b. The lower third of the uterus remains less active, promoting
downward passage of the fetus, muscle wall becomes
thinner
4. Cervical Changes
a. Effacement: thinning and shortening, drawn over the fetus
and amniotic sac, merges with the thinning lower uterine
segment
b. Dilation: opening, expressed in centimeters
c. Nullipara: this woman completes more cervical effacement
early in the process of cervical dilation, and dilation
happens at the end
d. Multipara: cervix is thicker at any given part of labor,
remains thick while continuing to dilate
ii. Cardiovascular system
1. During each contraction, the uterus pushes against the maternal
spinal arteries, temporarily shunting blood back into maternal
circulation, causing an increase in maternal blood volume.
2. Supine hypotension might occur, mother is encourages to lay on
her side
iii. Respiratory system
1. Depth and rate of respirations increase
2. Might experience respiratory alkalosis because of hyperventilation
iv. Gastrointestinal system
1. Gastric motility is reduced, so more n/v
2. Debated whether the laboring mother should be allowed nutrition
or if this is a bigger risk for aspiration
v. Urinary system
1. Reduced sensation of a full bladder
2. May inhibit fetal descent
vi. Hematopoietic system
, 1. About 500 mL of blood loss, but this is okay because the mother
has been producing more blood in order to compensate for this loss
2. Leukocytes may go up to 20,000 with no indications of infection
3. Fibrinogen continues to go up throughout the laboring process
a. Increased risk for venous thrombosis
b. Fetal Effects
i. Placental circulation
1. During contractions, blood flow is stopped from the placenta. The
fetus has several mechanisms to compensate:
a. Fetal Hgb takes on more O2 and releases more CO2 than
maternal Hgb
b. High Hgb levels in the fetus
c. High cardiac output
ii. Cardiovascular system
1. Reacts quickly to events in labor, FHR quickly changes within the
110-160 range
iii. Pulmonary system
1. Fetal lung fluid production decreases to 65% production and the
fluid gets absorbed. Some are expelled when the baby gets pushed
out.
2. Cardinal movements in labor
a. Descent
i. Movement of fetus through the birth canal
ii. Progress through maternal pelvis
b. Engagement/station
i. Fetal presenting part reaches “0” station (head at the pubic spine)
1. Negative numbers means the baby is above the engaged spot
c. Flexion
i. Because of resistance from musculature and pelvis, the head flexes so a
smaller diameter enters the pelvis
d. Internal rotation
1. Physiology of labor (for example: what happens when the uterus contracts)
a. Maternal effects
i. Reproductive system
1. Characteristics of contractions
a. Coordinated
i. Frequency: beginning of one uterine contraction to
the beginning of the next
ii. Duration: beginning of a uterine contraction to the
end of the same contraction
iii. Intensity: strength of a contraction (only tested
using an internal monitor)
b. Involuntary
i. Not under conscious control. The mother cannot
decide when to start or end the contraction
c. Intermittent
i. This allows for relaxation of the uterus and
resumption of blood flow back to the placenta
d. Interval
i. The period of time from the end of one contraction
to the beginning of the next
2. Contraction Cycle
a. Increment: period of increasing strength
b. Acme: The period during which the contraction is the most
intense
c. Decrement:The period of decreasing intensity as the uterus
relaxes
3. Uterine Muscle
a. The upper two thirds of the uterus contract actively to push
the fetus down, muscle wall becomes thicker
, b. The lower third of the uterus remains less active, promoting
downward passage of the fetus, muscle wall becomes
thinner
4. Cervical Changes
a. Effacement: thinning and shortening, drawn over the fetus
and amniotic sac, merges with the thinning lower uterine
segment
b. Dilation: opening, expressed in centimeters
c. Nullipara: this woman completes more cervical effacement
early in the process of cervical dilation, and dilation
happens at the end
d. Multipara: cervix is thicker at any given part of labor,
remains thick while continuing to dilate
ii. Cardiovascular system
1. During each contraction, the uterus pushes against the maternal
spinal arteries, temporarily shunting blood back into maternal
circulation, causing an increase in maternal blood volume.
2. Supine hypotension might occur, mother is encourages to lay on
her side
iii. Respiratory system
1. Depth and rate of respirations increase
2. Might experience respiratory alkalosis because of hyperventilation
iv. Gastrointestinal system
1. Gastric motility is reduced, so more n/v
2. Debated whether the laboring mother should be allowed nutrition
or if this is a bigger risk for aspiration
v. Urinary system
1. Reduced sensation of a full bladder
2. May inhibit fetal descent
vi. Hematopoietic system
, 1. About 500 mL of blood loss, but this is okay because the mother
has been producing more blood in order to compensate for this loss
2. Leukocytes may go up to 20,000 with no indications of infection
3. Fibrinogen continues to go up throughout the laboring process
a. Increased risk for venous thrombosis
b. Fetal Effects
i. Placental circulation
1. During contractions, blood flow is stopped from the placenta. The
fetus has several mechanisms to compensate:
a. Fetal Hgb takes on more O2 and releases more CO2 than
maternal Hgb
b. High Hgb levels in the fetus
c. High cardiac output
ii. Cardiovascular system
1. Reacts quickly to events in labor, FHR quickly changes within the
110-160 range
iii. Pulmonary system
1. Fetal lung fluid production decreases to 65% production and the
fluid gets absorbed. Some are expelled when the baby gets pushed
out.
2. Cardinal movements in labor
a. Descent
i. Movement of fetus through the birth canal
ii. Progress through maternal pelvis
b. Engagement/station
i. Fetal presenting part reaches “0” station (head at the pubic spine)
1. Negative numbers means the baby is above the engaged spot
c. Flexion
i. Because of resistance from musculature and pelvis, the head flexes so a
smaller diameter enters the pelvis
d. Internal rotation
