Dysfunctional Labor, Uterine Contractility, & Dystocia Flashcards
Physiology of uterine contraction
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
During labor, the uterus is physiologically divided into what 2 segments?
Upper segment — actively contracts and retracts to expel fetus
Lower segment + cervix — becomes thinner and more passive
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
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
Etiology of prolonged latent phase
Excess use of sedatives or analgesics
Fetal malposition
Management of protracted latent phase
Therapeutic rest (morphine) — can provide pt with relief and aid in distinction between true and false labor
Define protraction and arrest in active phase of first stage of labor in nulliparous vs. multiparous
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
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?
Inadequate uterine activity
Cephalopelvic disproportion
Fetal malposition
Anesthesia
_____ is defined as “difficult labor”, characterizing labor that is not progressing normally
Dystocia
Note: the diagnosis of dystocia should not be made before an adequate trial of labor has been tried
Dystocia results from abnormalities of the 3 P’s. What are the 3 P’s?
Power (uterine contractions or maternal expulsive forces)
Passenger (position, size, or presentation of the fetus)
Passage (maternal pelvic bone contractures)
Management of abnormalities in active phase of stage 1 labor
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
When assessing 3 P’s: power, passenger, passage: How is Power assessed?
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
When assessing 3 P’s: power, passenger, passage: what is the primary “passage” abnormality?
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
_____ and _____ pelvis’ have a good prognosis for vaginal delivery
Gynecoid; anthropoid
When assessing 3 P’s: power, passenger, passage: What are some causes of “passenger” abnormalities?
Presentations other than vertex occiput anterior (OA)
Macrosomia
Shoulder dystocia
Fetal anomalies (hydrocephalus, fetal ascites, enlargement of fetal organs, conjoined twins, locked twins)
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 ______
Transverse arrest of descent
Causes of persistent OT position
CPD, altered pelvic architecture (android or platypelloid), relaxed pelvic floor (epidural)
Management of persistent occipitotransverse (OT) position
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
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?
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
Define macrosomia
Fetus weighing 4500 grams
[Large for gestational age = birth weight equal to or greater than 90%]
Risk factors for macrosomia
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
Maternal complications from macrosomia
Primary risk is increased risk for C section
Postpartum hemorrhage and significant vaginal laceration
Fetal complications from macrosomia
Shoulder dystocia
Fracture of clavicle
Damage to nerves of brachial plexus
Types of brachial plexus injury that may occur with delivery of baby with macrosomia
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
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
Prophylactic C section
Delivery that requires additional obstetric maneuvers following failure of gentle downward traction on the fetal head to effect delivery of the shoulders
Shoulder dystocia
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?
Retraction of delivered fetal head against maternal perineum
Antepartum risk factors for shoulder dystocia
Fetal macrosomia Maternal diabetes Obesity Post-term gestation Short stature Previous hx of macrosomic birth Previous hx of shoulder dystocia
Labor-associated risk factors for shoulder dystocia
Labor induction
Epidural analgesia
Prolonged labor
Operative vaginal deliveries
Neonatal complications from shoulder dystocia
Brachial plexus injuries
Fractured clavicle or humerus
Hypoxic-ischemic encephalopathy
Death
Management of shoulder dystocia
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
2 types of rotational maneuvers for shoulder dystocia
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
