Clin: Dysfunctional Labor, Uterine Contractility and Dystocia - Moulton

Question 1

what triggers an enzymatic process that results in the formation of the actin-myosin element in the uterus?

Answer 1

billions of smooth muscle cells form contractile units

- when intracellular ionic calcium concentration increases it triggers the formation of actin-myosin elements

Question 2

stimulation of oxytocin receptors on the plasma membrane does what?

Answer 2

further activates the actin-myosin element

Question 3

where do contractions occur?

Answer 3

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

Question 4

coordinated smooth muscle cell contractions are secondary to what?

Answer 4

gap junctions that activate the movement of action potentials throughout the myometrium

Question 5

what maintains relaxation?

Answer 5

factors that increase cAMP

Question 6

what causes contraction?

Answer 6

increase of intracellular calcium stores

- promote interaction of actin and myosin causing uterine contractions

Question 7

what are the two distinct segments of the uterus that are formed during labor?

Answer 7

1. the upper segment: actively contracts and retracts to expel the fetus
2. the lower segment along with the cervix: becomes thinner and passive

Question 8

what physiologic changes are seen in the cervix during labor?

Answer 8

it changes from a firm, in-tact sphincter to soft, pliable, dilatable structure
- these changes are the result of collagenolysis, increase in hyaluronic acid, decrease in dermatan sulfate, which favors water content

Question 9

the presence of regular uterine contractions of sufficient intensity, frequency and duration to bring about demonstrable effacement and dilation of the cervix

Answer 9

labor

Question 10

onset of contractions to full dilation

Answer 10

first stage

Question 11

full dilation of cervix to delivery of the infant

Answer 11

second stage

Question 12

delivery of infant to delivery or placenta

Answer 12

third stage

Question 13

cervical softening effacement occurs with minimal dilation (<6cm)

Answer 13

latent phase

Question 14

this phase starts when cervix is dilated to 6cm

• includes both cervical dilation and ultimately, descent of the presenting fetal part
• acceleration phase, also deceleration phase

Answer 14

active phase

Question 15

protraction

Answer 15

when contraction is slower than normal rate

Question 16

arrest

Answer 16

complete cessation of progress (no further dilation or decent)

Question 17

what does an arrested latent phase imply?

Answer 17

labor has not begun

Question 18

what are the normal limits of the latent phase?

Answer 18

nuliparous: up to 20hs

mulitparous up to 14 hrs

Question 19

what is the tx of the latent phase?

Answer 19

• terapeutic rest
• can give pt relief air between true and false labor
• morhphine -> 62-85% of pts will progress to active phase
• 10-29% will stop having contractions and diagnosis of false labor can be made

Question 20

what are the normal limits of cervical dilation in the active phase?

Answer 20

nulliparous: cervical dilation 1.2cm/hr
multiparous: cervical dilation of 1.5cm/hr

NOTE: cervical dilation LESS than normal = protraction disorder of dilation of active
- if 2+ hours elapse with NO cervical dilation = arrest of dilation

Question 21

what are the normal limits of fetal descent?

Answer 21

nulliparous: 1cm/hr
multiparous: 2cm/hr

NOTE: fetal descent LESS than normal = protraction of descent of active phase
- if no change in descent/station has occurred within 1hr, arrest of descent has occurred

Question 22

“difficult labor”, results from abnormalities of the 3 P’s:

Answer 22

1. power (uterine contractions or maternal expulsive0
2. passenger (position, size, or presentation of fetus)
3. passage (maternal pelvic bone contractures)

Question 23

the dx of dystocia should NOT be made before what?

Answer 23

adequate trial of labor has been tried

Question 24

stimulation of uterine contraction when spontaneous contractions have failure to result in progressive cervical dilation or descent of the fetus

Answer 24

augmentation

- **consider augmenting if contractions are less than 3/1 minutes

Question 25

ACOOG recommends oxytocin in protraction and arrest disorders after assessing what?

Answer 25

- maternal pelvis - fetal position - station - maternal and fetal status

Question 26

what are the benefits of AROM?

Answer 26

augment labor, allows assessment of meconium status

Question 27

what are the risks of AROM?

Answer 27

cord prolapse, prolonged rupture associated with chorioanmionitis

Question 28

3 contractions in a 10 minute period averaging 25mmHg above baseline

Answer 28

minimal effective uterine activity

Question 29

calculated by measuring the peaks of contractions in mmHg in a 10 min period

Answer 29

``` montevideo units (MVU) >200MVU for at least 2 hours - before proceeding to cesarean section, should document adequate contractions at least 4 hours ```

Question 30

what is the only FDA approved medicine for labor augmentation

Answer 30

pitocin | - 80% of pts with documented disorder of labor will respond to oxytocin with progression of labor and vaginal delivery

Question 31

what is the MOA of pitocin?

Answer 31

stimulates uterine contractions - increases intracellular calcium -> results in increase in actin and myosin activity - sensitivity of the uterus to oxytocin increases between 20-40 gestational weeks

Question 32

labor induction?!

Answer 32

MISOPROSTOL

Question 33

labor augmentation?!

Answer 33

PITOCIN

Question 34

how much time is needed for full effect of pitocin to be evident in a contraction pattern?

Answer 34

20-30 mins

Question 35

refers to a disparity between the size of maternal pelvis and the fetal head that precludes vaginal delivery - causes a failure of descent and sometimes engagement of the head - nulliparous women who present in labor with an unengaged head indicates an increased likelihood of this

Answer 35

cephalopelvic disproportion (CPD)

Question 36

which pelvic shapes have a good prognosis for delivery?

Answer 36

gynecoid and anthropoid - pubic arch >90 - ischial tuberosity >8.5cm - diagonal conjugate >11.5cm - prominence of ischial spines

Question 37

what position does the fetal head usually enter and engage the maternal pelvis?

Answer 37

occipitotransverse (OT) position | - then rotates to OA or OP

Question 38

what can cause shoulder dystocia?

Answer 38

abnormalities of the fetal structure - macrosomia - fetal anomalies

Question 39

this occurs when the head fails to rotate and flex into the OA position - may be caused by CPD, altered pelvic architecture (android or platypelloid pelvis), or relaxed pelvic floor (epidural)

Answer 39

persistent occipitotransverse (OT) position

Question 40

OT with arrest of descent for 1 hr or more is know as what?

Answer 40

transverse arrest of descent - arrest occurs because of the deflexion that occurs with persistent OT position the occipital diameter (11cm) becomes the presenting diameter (seen commonly at +1 - +2 stations

Question 41

what is the management of persistent OT if: - pelvis is adequate - infant is not macrosomic - contractions are inadequate

Answer 41

- start pitocin | - rotate: manually or with forceps

Question 42

how do you manage an OT position if pelvis is inadequate or infant is deemed macrosomic?

Answer 42

cesarean is indicated

Question 43

even if the head rotates to OP initially, the majority will eventually rotate to what position?

Answer 43

OA spontaneously - only 5-15% will stay OP - course of labor in OP is usually normal (second stage may be prolonged, associated with more back pain for mom)

Question 44

fetus weighing > 4500g

Answer 44

macrosomia

Question 45

birth weight equal to or greater than 90% for a given gestational age

Answer 45

large for gestational age (LGA) - 37 wks: 90% = 3,755g - 40 wks: 90% = 4,060g - 42 wks: 90% = 4,098g

Question 46

is diagnosis of fetal macrosmia with ultrasound precise?

Answer 46

NO!

Question 47

what can be seen by ultrasound, and makes vaginal delivery impossible?

Answer 47

hydrocephalus

Question 48

what can result in dystocia secondary to enlarged fetal abdomen?

Answer 48

fetal ascites or enlargement of fetal organs (liver) - immune hydrops (Rh isoimmunization) most common - nonimmune hydrops caused by congenital infections, chromosomal abnormalities or fetal arrhythmias

Question 49

what are locked twins?

Answer 49

baby A breech, baby B vertex

Question 50

what are the 3 P's??

Answer 50

- power - passage - passenger

Question 51

what are the risk factors for macrosomia?

Answer 51

- maternal diabetes - previous history of macrosomia - maternal pre-pregnancy obesity - weight gain during pregnancy - multiparity - gestational age >40 - maternal birth weight - maternal age <17 years old - +50g glucose screen with a negative result on 3hr

Question 52

what are risk factors for fetal morbidity/mortality associated with macrosomia?

Answer 52

- shoulder dystocia - fracture of clavicle - damage to brachial plexus NOTE: risk of brachial plexus injuries among vaginal deliveries increase 21x when birth weight > 4500g

Question 53

upper arm palsy - most common brachial plexus injury - caused by injury to C5-6

Answer 53

Erb-Duschenne palsy

Question 54

lower arm palsy | - caused by damage to C8 and T1

Answer 54

Klumpke palsy

Question 55

what will damage to all 4 nerve roots cause?

Answer 55

paralysis of entire arm

Question 56

ACOG recommends prophylactic cesarean for estimated fetal weight of what?

Answer 56

>5000g in non diabetic pt | >4500g in diabetic pt

Question 57

retraction of delivered fetal head against the maternal perineum

Answer 57

turtle sign

Question 58

what are the antepartum risk factors for shoulder dystocia?

Answer 58

- fetal macrosomia - maternad diabetes - obesity - post term gestation - short stature - previous hx of macrosomic birth - previous hx of shoulder dystocia

Question 59

what are the risk factors for should dystocia during labor?

Answer 59

- labor induction - epidural analgesia - prolonged labor - operative vaginal deliveries

Question 60

what are the neonatal risks associated with shoulder dystocia?

Answer 60

- brachial plexus injuries (less than 10% result in permanent disability) - fractured clavicle or humerus - hypoxic-ischemic encephalopathy - death

Question 61

hyperflexion and abduction of the maternal hips

Answer 61

McRobert's maneuver

Question 62

putting pressure where, may dislodge the impacted anterior should?

Answer 62

suprapubic pressure | - do NOT apply fundal pressure

Question 63

cephalic replacement - **last resort** - poor prognosis, significant risk of fetal morbidity/mortality

Answer 63

Zavanelli maneuver - fetal head is manually returned to it's prerestitution position - slowly replaced in the vagina by steady upward pressure - delivery is by **emergent c-section**

Question 64

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

Answer 64

Rubin maneuver

Question 65

apply pressure behind the posterior (free) shoulder to rotate the infant and dislodge the anterior shoulder

Answer 65

Wood's corkscrew maneuver

Question 66

obstetric emergency - call for help! (anesthesia, NICU) - can not be predicted or prevented and most occur in the absence of macrosomia

Answer 66

shoulder dystocia

Question 67

what are the initial maneuvers for shoulder dystocia?

Answer 67

McRobert's and suprapubic pressure