Dysfunctional Labor, Uterine Contractility, & Dystocia

Question 1

Physiology of uterine contraction

Answer 1

Each smooth muscle cell of the uterus becomes a contractile element when intracellular Ca increases to trigger formation of actin-myosin element

Stimulation of ocytocin receptors on plasma membrane further activates actin-myosin element

Contractions occur in localized areas during gestation, but during labor the entire uterus contracts in an organized fashion

Question 2

During labor, the uterus is physiologically divided into what 2 segments?

Answer 2

Upper segment — actively contracts and retracts to expel fetus

Lower segment + cervix — becomes thinner and more passive

Question 3

Abnormalities in the phases of labor may be termed “protraction” which is slower than normal, or arrest which is a complete cessation of progress. However, the latent phase is typically only referred to as protraction (arrest in this phase implies labor has not begun). Define protraction of latent phase in nulliparous vs. multiparous and the effect this protraction has on perinatal mortality

Answer 3

Protraction of latent phase is defined as >20 hrs in nulliparous, or >14 hrs in multiparous

The outcome of prolonged latent phase has little effect on perinatal mortality

Question 4

Etiology of prolonged latent phase

Answer 4

Excess use of sedatives or analgesics

Fetal malposition

Question 5

Management of protracted latent phase

Answer 5

Therapeutic rest (morphine) — can provide pt with relief and aid in distinction between true and false labor

Question 6

Define protraction and arrest in active phase of first stage of labor in nulliparous vs. multiparous

Answer 6

Protraction in nulliparous: cervical dilation <1.2cm/hr, fetal descent <1cm/hr

Protraction in multiparous: cervical dilation <1.5cm/hr, fetal descent <2cm/hr

Arrest: 2+ hours with no cervical dilation, no change in descent/station in 1 hr

Question 7

While protraction of the latent phase of stage 1 labor do not increase risk of perinatal mortality, abnormalities in the active phase of stage 1 can increase perinatal mortality.

What are some etiologies of active phase labor abnormalities?

Answer 7

Inadequate uterine activity

Cephalopelvic disproportion

Fetal malposition

Anesthesia

Question 8

_____ is defined as “difficult labor”, characterizing labor that is not progressing normally

Answer 8

Dystocia

Note: the diagnosis of dystocia should not be made before an adequate trial of labor has been tried

Question 9

Dystocia results from abnormalities of the 3 P’s. What are the 3 P’s?

Answer 9

Power (uterine contractions or maternal expulsive forces)

Passenger (position, size, or presentation of the fetus)

Passage (maternal pelvic bone contractures)

Question 10

Management of abnormalities in active phase of stage 1 labor

Answer 10

Consider augmenting if contractions are less than 3 in 10 min period and/or intensity is <25 mmHg

ACOG recommends Oxytocin in protraction and arrest disorders after assessing maternal pelvis, fetal position, station, maternal and fetal status

Question 11

When assessing 3 P’s: power, passenger, passage: How is Power assessed?

Answer 11

IUPC (remember this requires rupture of membranes)

—calculates contraction strength in MVUs, >200 MVUs in 2 hours means pitocin is unnecessary, adequate contractions must be documented for at least 4 hours before proceeding to C section

Question 12

When assessing 3 P’s: power, passenger, passage: what is the primary “passage” abnormality?

Answer 12

Cephalopelvic disproportion (CPD) — disparity b/w size of maternal pelvis and fetal head

Nulliparous women who present in labor with an unengaged head indicate increased likelihood of CPD

Question 13

_____ and _____ pelvis’ have a good prognosis for vaginal delivery

Answer 13

Gynecoid; anthropoid

Question 14

When assessing 3 P’s: power, passenger, passage: What are some causes of “passenger” abnormalities?

Answer 14

Presentations other than vertex occiput anterior (OA)

Macrosomia

Shoulder dystocia

Fetal anomalies (hydrocephalus, fetal ascites, enlargement of fetal organs, conjoined twins, locked twins)

Question 15

During normal fetal delivery, the fetal head usually enters and engages the maternal pelvis in OT position, then rotates to OA. A persistent OT position with arrest of descent for a period of 1+ hrs is known as ______

Answer 15

Transverse arrest of descent

Question 16

Causes of persistent OT position

Answer 16

CPD, altered pelvic architecture (android or platypelloid), relaxed pelvic floor (epidural)

Question 17

Management of persistent occipitotransverse (OT) position

Answer 17

If pelvis is adequate, infant is not macrosomic, and contractions are inadequate: start oxytocin, rotation maneuvers can be done manually or with Keilland forceps

If pelvis is inadequate or infant deemed to be macrosomic, proceed with C section

Question 18

Persistent OP position usually results in a normal course of labor, although the second stage may be prolonged, and pt may complain of more severe back pain. How is delivery for persistent OP managed?

Answer 18

Observation of a prolonged second stage of labor is appropriate if it continues to progress and fetal heart rate is normal; delivery of head often occurs spontaneously

Operative vaginal delivery is also an option — vacuum or forceps

Question 19

Define macrosomia

Answer 19

Fetus weighing 4500 grams

[Large for gestational age = birth weight equal to or greater than 90%]

Question 20

Risk factors for macrosomia

Answer 20

Maternal diabetes
Hx of macrosomia
Pre-pregnancy obesity
Weight gain during pregnancy
Multiparity
Male fetus
Gestational age >40wks
Ethnicity
Maternal birth weight
Maternal height
Maternal age <17 y/o
\+50g glucose screen w/ negative result on 3 hr

Question 21

Maternal complications from macrosomia

Answer 21

Primary risk is increased risk for C section

Postpartum hemorrhage and significant vaginal laceration

Question 22

Fetal complications from macrosomia

Answer 22

Shoulder dystocia

Fracture of clavicle

Damage to nerves of brachial plexus

Question 23

Types of brachial plexus injury that may occur with delivery of baby with macrosomia

Answer 23

MOST COMMON = Erb-Duschenne — upper arm palsy, caused by injury to C5-6

Klumpke — lower arm palsy, caused by damage to C8 and T1

Paralysis of entire arm — damage to all 4 nerve roots

Question 24

Because the risk of morbidity for infants and mothers increases significantly as weight increases, ACOG recommends _______ for estimated fetal weight of >5000g in nondiabetic pts, and >4500g in diabetic pts

Answer 24

Prophylactic C section

Question 25

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

Answer 25

Shoulder dystocia

Question 26

Shoulder dystocia is caused by the impaction of the anterior fetal shoulder behind the maternal pubic symphysis, or impaction of the posterior shoulder on the sacral promontory. It may present with turtle sign — what is turtle sign?

Answer 26

Retraction of delivered fetal head against maternal perineum

Question 27

Antepartum risk factors for shoulder dystocia

Answer 27

Fetal macrosomia
Maternal diabetes
Obesity
Post-term gestation
Short stature
Previous hx of macrosomic birth
Previous hx of shoulder dystocia

Question 28

Labor-associated risk factors for shoulder dystocia

Answer 28

Labor induction
Epidural analgesia
Prolonged labor
Operative vaginal deliveries

Question 29

Neonatal complications from shoulder dystocia

Answer 29

Brachial plexus injuries

Fractured clavicle or humerus

Hypoxic-ischemic encephalopathy

Death

Question 30

Management of shoulder dystocia

Answer 30

McRobert’s maneuver = hyperflexion and abduction of maternal hips

Suprapubic pressure — may dislodge impacted anterior shoulder (DO NOT APPLY FUNDAL PRESSURE)

If above fails: Rotational maneuvers, delivery of posterior fetal arm, fracturing fetal clavicle, proctoepisiotomy, Zavanelli maneuver (cephalic replacement, this is last resort)

Call for help — anesthesiologist and NICU

Question 31

2 types of rotational maneuvers for shoulder dystocia

Answer 31

Rubin maneuver — place pressure on an accessible shoulder to push it toward the anterior chest wall of the fetus to decrease bisacrominal diameter and free the impacted shoulder

Wood’s corkscrew maneuver — apply pressure behind posterior to rotate infant and dislodge anterior shoulder