Dysfunctional Labor Flashcards
How does a uterine contraction occur?
Oxytocin binds the Gq receptor and increases intracellular [Ca++] which promotes actin-myosin interaction and leads to uterine contractions.
How does uterine relaxation maintained?
There are factors that increase intracellular [cAMP] that leads to relaxation.
During labor, what occurs in the upper segment and the lower segment of the uterus?
The upper segment actively contracts and retracts to expel the fetus.
The lower segment (along with the cervix) becomes thinner and passive.
How does the cervix become thinner and softened during labor?
The cervix contains collagen and SM. Therefore, collagenolysis (increased hyaluronic acid) and decreased dermatan sulfate which favors increased water content.
Define the following stages of labor:
First stage (latent and active)
Second stage
Third stage
Fourth stage
1st stage: onset of contractions to full cervical dilation.
- latent: cervical softening and effacement with minimal dilation.
- active: begins when cervix id dilated to 4 cm. There is an increased rate of dilation and initial presentation.
2nd stage: full dilation to delivery of the infant.
3rd stage: delivery of the infant to delivery of the placenta.
4th stage: postpartum care
What is arrest of labor vs. protraction in labor?
Arrest - complete cessation of progression (no further dilation or descent)
Protraction - slower than normal rate
Dysfunctional labor =
Rates of dilation and descent > times of normal labor pattern
What are the normal limit of the latent phase in nulliparous vs. multiparous pregnancies?
What can cause a prolonged (abnormal) latent phase?
What is the outcome if this occurs?
Nulliparous: up to 20 hrs.
Multiparous: up to 14 hrs.
(1) Most common are patients who have entered labor without significant cervical change. (2) Excessive sedative/analgesic use. (3) Fetal malposition.
The outcome is usually normal.
How is a prolonged latent phase managed?
Therapeutic rest (sleep)
If needed, pain relief can be provided and aid in distinction between true and false labor (Morphine 15-20 mg). Most patients will progress to active phase, some will cease contracting (false labor) and very few will fail and delivery with pitocin might be indicated.
What is the normal limit of the active phase in nulliparous vs. multiparous pregnancies?
What constitutes cervical protraction vs. arrest?
What is the normal limits of fetal descent in nulliparous vs. multiparous pregnancies?
What constitutes cervical protraction vs. arrest?
Nulliparous: 1.2 cm/hr
Multiparous: 1.5 cm/hr
Protraction is cervical dilation less than normal. Arrest is diagnosed when 2 or more hrs. have elapsed with no cervical dilation.
Nulliparous: 1 cm/hr
Multiparous: 2 cm/hr
Protraction is descent less than normal. Arrest is diagnosed if no change in decsent/station has occured within 1 hr.
What is the outcome of abnormalities in the active phase?
What can cause it? (4)
It may have an increased risk of perinatal mortality.
Inadequate uterine activity, cephalopelvic disproportion, fetal malposition, anesthesia.
What are the 3 P’s of the active phase?
Power - uterine contractions or maternal expulsive forces
Passenger - position, size, or presentation of the fetus
Passage - maternal pelvic bone contractures
Dystocia =
When can it be diagnosed?
Dystocia = “difficult labor”. It can be used interchangeably with dysfunctional labor.
It can only be diagnosed if an adequate trial of labor has been done.
Augmentation =
When should it be considered?
Augmentation = stimulation of uterine contraction when spontaneous contractions have failed to result in progression cervical dilation or descent of the fetus.
It should be considered if contractions are less than 3 in a 10 min. period and/or the intensity is < 25 mmHg.
ACOG recommends oxytocin in protraction and arrest disorders after assessing: (4)
Maternal pelvis
Fetal position
Station
Maternal and fetal status
How can “power” be evaluated in the active phase? (2)
IUPC - placed transcervically and gives a precise measurement of intensity of uterine contractions.
-it requires AROM (good in that it augments labor and allows meconium analysis, bad in that it increases risk for cord prolapse and choramnionitis).
Montevideo units (MVU) - measures the peaks of contractions in mmHg in a 10 min period (we want > 200 MVU in past 2 hrs.)
How is “minimal effective uterine activity” defined?
3 uterine contractions in a 10 minute period averaging 25 mmHg above baseline (approx. 20 mmHg).
How is the “passage” evaluated in the active phase? (2)
Cephalopelvic disproportion (CPD) - refers to a disparity between the size of the maternal pelvis and the fetal head that precludes vaginal delivery.
Evaluation of the pelvis: gynecoid and anthropoid pelves are good prognoses.
- pubic arch > 90 degrees
- ischial tuberosity > 8.5 cm
- diagonal conjugate > 11.5 cm
- evaluate prominence of ischial spines
What is assessed in the “passenger” evaluation in the active phase?
The presentation of the baby - should be OA
What kind of fetal structural abnormalities can cause dystocia? (3)
Macrosomia
Shoulder dystocia
Fetal anomalies
What is a persistent occipitotransverse (OT) position?
What can cause it? (3)
What is “transverse arrest of descent”?
Occurs when the head fails to rotate and flex into the OA position.
CPD, altered pelvic architecture (android or platypelloid pelvis) or relaxed pelvic floor (epidural).
A persistent OT position with arrest of descent for a period of 1 hr or more.
If the pelvis is adequate, the infant is not macrosomic and contractions are inadequate, how should the persistent OT position be managed?
What if the pelvis is inadequate or infant is macrosomic?
Start oxytocin and try to rotate (manually or with forceps)
Proceed with a C-section
What is the outcome if the OT position is not persistent and fetal HR is normal?
The outcome is typically fine - observation of the prolonged 2nd stage is appropriate and delivery of the head occurs spontaneously
At what weight is macrosomia diagnosed?
What is large for gestational age (LGA)?
4500 g
Birth weight equal or greater than the 90th percentile for a given gestational age
