Clin: Dysfunctional Labor, Uterine Contractility and Dystocia - Moulton Flashcards
what triggers an enzymatic process that results in the formation of the actin-myosin element in the uterus?
billions of smooth muscle cells form contractile units
- when intracellular ionic calcium concentration increases it triggers the formation of actin-myosin elements
stimulation of oxytocin receptors on the plasma membrane does what?
further activates the actin-myosin element
where do contractions occur?
in localized areas during gestation, but during labor the entire uterus contracts in an organized fashion
coordinated smooth muscle cell contractions are secondary to what?
gap junctions that activate the movement of action potentials throughout the myometrium
what maintains relaxation?
factors that increase cAMP
what causes contraction?
increase of intracellular calcium stores
- promote interaction of actin and myosin causing uterine contractions
what are the two distinct segments of the uterus that are formed during labor?
- the upper segment: actively contracts and retracts to expel the fetus
- the lower segment along with the cervix: becomes thinner and passive
what physiologic changes are seen in the cervix during labor?
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
the presence of regular uterine contractions of sufficient intensity, frequency and duration to bring about demonstrable effacement and dilation of the cervix
labor
onset of contractions to full dilation
first stage
full dilation of cervix to delivery of the infant
second stage
delivery of infant to delivery or placenta
third stage
cervical softening effacement occurs with minimal dilation (<6cm)
latent phase
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
active phase
protraction
when contraction is slower than normal rate
arrest
complete cessation of progress (no further dilation or decent)
what does an arrested latent phase imply?
labor has not begun
what are the normal limits of the latent phase?
nuliparous: up to 20hs
mulitparous up to 14 hrs
what is the tx of the latent phase?
- 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
what are the normal limits of cervical dilation in the active phase?
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
what are the normal limits of fetal descent?
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
“difficult labor”, results from abnormalities of the 3 P’s:
- power (uterine contractions or maternal expulsive0
- passenger (position, size, or presentation of fetus)
- passage (maternal pelvic bone contractures)
the dx of dystocia should NOT be made before what?
adequate trial of labor has been tried
stimulation of uterine contraction when spontaneous contractions have failure to result in progressive cervical dilation or descent of the fetus
augmentation
- **consider augmenting if contractions are less than 3/1 minutes
ACOOG recommends oxytocin in protraction and arrest disorders after assessing what?
- maternal pelvis
- fetal position
- station
- maternal and fetal status
what are the benefits of AROM?
augment labor, allows assessment of meconium status
what are the risks of AROM?
cord prolapse, prolonged rupture associated with chorioanmionitis
3 contractions in a 10 minute period averaging 25mmHg above baseline
minimal effective uterine activity
calculated by measuring the peaks of contractions in mmHg in a 10 min period
montevideo units (MVU) >200MVU for at least 2 hours - before proceeding to cesarean section, should document adequate contractions at least 4 hours
what is the only FDA approved medicine for labor augmentation
pitocin
- 80% of pts with documented disorder of labor will respond to oxytocin with progression of labor and vaginal delivery
what is the MOA of pitocin?
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
labor induction?!
MISOPROSTOL
labor augmentation?!
PITOCIN
how much time is needed for full effect of pitocin to be evident in a contraction pattern?
20-30 mins
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
cephalopelvic disproportion (CPD)
which pelvic shapes have a good prognosis for delivery?
gynecoid and anthropoid
- pubic arch >90
- ischial tuberosity >8.5cm
- diagonal conjugate >11.5cm
- prominence of ischial spines
what position does the fetal head usually enter and engage the maternal pelvis?
occipitotransverse (OT) position
- then rotates to OA or OP
what can cause shoulder dystocia?
abnormalities of the fetal structure
- macrosomia
- fetal anomalies
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)
persistent occipitotransverse (OT) position
OT with arrest of descent for 1 hr or more is know as what?
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
what is the management of persistent OT if:
- pelvis is adequate
- infant is not macrosomic
- contractions are inadequate
- start pitocin
- rotate: manually or with forceps
how do you manage an OT position if pelvis is inadequate or infant is deemed macrosomic?
cesarean is indicated
even if the head rotates to OP initially, the majority will eventually rotate to what position?
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)
fetus weighing > 4500g
macrosomia
birth weight equal to or greater than 90% for a given gestational age
large for gestational age (LGA)
- 37 wks: 90% = 3,755g
- 40 wks: 90% = 4,060g
- 42 wks: 90% = 4,098g
is diagnosis of fetal macrosmia with ultrasound precise?
NO!
what can be seen by ultrasound, and makes vaginal delivery impossible?
hydrocephalus
what can result in dystocia secondary to enlarged fetal abdomen?
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
what are locked twins?
baby A breech, baby B vertex
what are the 3 P’s??
- power
- passage
- passenger
what are the risk factors for macrosomia?
- 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
what are risk factors for fetal morbidity/mortality associated with macrosomia?
- shoulder dystocia
- fracture of clavicle
- damage to brachial plexus
NOTE: risk of brachial plexus injuries among vaginal deliveries increase 21x when birth weight > 4500g
upper arm palsy
- most common brachial plexus injury
- caused by injury to C5-6
Erb-Duschenne palsy
lower arm palsy
- caused by damage to C8 and T1
Klumpke palsy
what will damage to all 4 nerve roots cause?
paralysis of entire arm
ACOG recommends prophylactic cesarean for estimated fetal weight of what?
> 5000g in non diabetic pt
>4500g in diabetic pt
retraction of delivered fetal head against the maternal perineum
turtle sign
what are the antepartum risk factors for shoulder dystocia?
- fetal macrosomia
- maternad diabetes
- obesity
- post term gestation
- short stature
- previous hx of macrosomic birth
- previous hx of shoulder dystocia
what are the risk factors for should dystocia during labor?
- labor induction
- epidural analgesia
- prolonged labor
- operative vaginal deliveries
what are the neonatal risks associated with shoulder dystocia?
- brachial plexus injuries (less than 10% result in permanent disability)
- fractured clavicle or humerus
- hypoxic-ischemic encephalopathy
- death
hyperflexion and abduction of the maternal hips
McRobert’s maneuver
putting pressure where, may dislodge the impacted anterior should?
suprapubic pressure
- do NOT apply fundal pressure
cephalic replacement
- last resort
- poor prognosis, significant risk of fetal morbidity/mortality
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
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
Rubin maneuver
apply pressure behind the posterior (free) shoulder to rotate the infant and dislodge the anterior shoulder
Wood’s corkscrew maneuver
obstetric emergency
- call for help! (anesthesia, NICU)
- can not be predicted or prevented and most occur in the absence of macrosomia
shoulder dystocia
what are the initial maneuvers for shoulder dystocia?
McRobert’s and suprapubic pressure
