Dysfunctional Labor

Question 1

How does a uterine contraction occur?

Answer 1

Oxytocin binds the Gq receptor and increases intracellular [Ca++] which promotes actin-myosin interaction and leads to uterine contractions.

Question 2

How does uterine relaxation maintained?

Answer 2

There are factors that increase intracellular [cAMP] that leads to relaxation.

Question 3

During labor, what occurs in the upper segment and the lower segment of the uterus?

Answer 3

The upper segment actively contracts and retracts to expel the fetus.

The lower segment (along with the cervix) becomes thinner and passive.

Question 4

How does the cervix become thinner and softened during labor?

Answer 4

The cervix contains collagen and SM. Therefore, collagenolysis (increased hyaluronic acid) and decreased dermatan sulfate which favors increased water content.

Question 5

Define the following stages of labor:

First stage (latent and active)

Second stage

Third stage

Fourth stage

Answer 5

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

Question 6

What is arrest of labor vs. protraction in labor?

Answer 6

Arrest - complete cessation of progression (no further dilation or descent)

Protraction - slower than normal rate

Question 7

Dysfunctional labor =

Answer 7

Rates of dilation and descent > times of normal labor pattern

Question 8

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?

Answer 8

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.

Question 9

How is a prolonged latent phase managed?

Answer 9

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.

Question 10

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?

Answer 10

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.

Question 11

What is the outcome of abnormalities in the active phase?

What can cause it? (4)

Answer 11

It may have an increased risk of perinatal mortality.

Inadequate uterine activity, cephalopelvic disproportion, fetal malposition, anesthesia.

Question 12

What are the 3 P’s of the active phase?

Answer 12

Power - uterine contractions or maternal expulsive forces

Passenger - position, size, or presentation of the fetus

Passage - maternal pelvic bone contractures

Question 13

Dystocia =

When can it be diagnosed?

Answer 13

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.

Question 14

Augmentation =

When should it be considered?

Answer 14

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.

Question 15

ACOG recommends oxytocin in protraction and arrest disorders after assessing: (4)

Answer 15

Maternal pelvis
Fetal position
Station
Maternal and fetal status

Question 16

How can “power” be evaluated in the active phase? (2)

Answer 16

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.)

Question 17

How is “minimal effective uterine activity” defined?

Answer 17

3 uterine contractions in a 10 minute period averaging 25 mmHg above baseline (approx. 20 mmHg).

Question 18

How is the “passage” evaluated in the active phase? (2)

Answer 18

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

Question 19

What is assessed in the “passenger” evaluation in the active phase?

Answer 19

The presentation of the baby - should be OA

Question 20

What kind of fetal structural abnormalities can cause dystocia? (3)

Answer 20

Macrosomia
Shoulder dystocia
Fetal anomalies

Question 21

What is a persistent occipitotransverse (OT) position?

What can cause it? (3)

What is “transverse arrest of descent”?

Answer 21

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.

Question 22

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?

Answer 22

Start oxytocin and try to rotate (manually or with forceps)

Proceed with a C-section

Question 23

What is the outcome if the OT position is not persistent and fetal HR is normal?

Answer 23

The outcome is typically fine - observation of the prolonged 2nd stage is appropriate and delivery of the head occurs spontaneously

Question 24

At what weight is macrosomia diagnosed?

What is large for gestational age (LGA)?

Answer 24

4500 g

Birth weight equal or greater than the 90th percentile for a given gestational age

Question 25

What fetal anomalies can cause macrosomia? (3)

Answer 25

Hydrocephalus (seen on US)

Fetal ascites or organ enlargement (immune hydrops, non-immune hydrops)

Conjoined twins, locked twins (baby A is breech, baby B is vertex, etc.)

Question 26

What are some risk factors for macrosomia?

Answer 26

Maternal DM
H/O macrosomia
Pre-pregnancy obesity
Abnormal weight gain in pregnancy
Multiparity
Male fetus
Gestational age > 40 wks
Maternal height
Maternal age < 17 y/o
\+50 g glucose screen with negative 3 hr screen

Question 27

What are some associated risk factors of maternal and fetal macrosomia?

Answer 27

Maternal morbidity

• C-section
• Postpartum hemorrhage
• Vaginal lacerations

Fetal morbidity and mortality

• Shoulder dystocia
• Clavicle fx
• Damage to brachial plexus

Question 28

Erb-Duschenne palsy

Answer 28

Most common brachial plexus injury

Upper arm palsy
Injury to C5 and C6

Question 29

Klumpke palsy

Answer 29

Lower arm palsy

Injury to C8 and T1

Question 30

What causes paralysis of the entire arm?

Answer 30

Damage to all 4 nerve roots

Question 31

What weights does ACOG recommend prophylactic C-section in diabetic and non-diabetic patients?

Answer 31

Non-diabetic: > 5000 g

Diabetic: > 4500 g

Question 32

What is shoulder dystocia?

What causes it?

Answer 32

A delivery that requires additional obstetric maneuvers following failure of gentle downward traction on the fetal head to effect delivery of the shoulders.

The anterior fetal shoulder is impacted behind the maternal pubic symphysis or the posterior shoulder on the sacral promontory.

Question 33

What is Turtle sign?

Answer 33

Retraction of the delivered fetal head against the maternal perineum

Question 34

How can shoulder dystocia be managed with the following modalities?

McRobert’s maneuver (define)

Suprapubic pressure (define)

Rotational maneuvers, delivery of posterior fetal arm, fracture fetal clavicle

Proctoepisiotomy

Zavanelli maneuver (define)

Answer 34

McRobert’s maneuver: hyperflexion and abduction of the maternal hips

Suprapubic pressure: may dislodge the impacted shoulder. DO NOT apply fundal pressure.

Rotational maneuvers, delivery of posterior fetal arm, fracture fetal clavicle

Proctoepisiotomy

Zavanelli maneuver: cephalic replacement and C-section, last resort, poor prognosis with significant fetal morbidity/mortality

Question 35

Define the following rotational maneuvers for shoulder dystocia:

Rubin maneuver

Wood’s corkscrew maneuver

Answer 35

Rubin - place pressure on an accessible shoulder to push it toward the anterior chest wall of the fetus to decrease the bisacromial diameter and free the impacted shoulder.

Wood’s corkscrew - apply pressure behind the posterior head to rotate the infant and dislodge the anterior shoulder.

Question 36

Shoulder dystocia is an…

What are the initial maneuvers to try?

Answer 36

Obstetric emergency

McRobert’s maneuver and suprapubic pressure