Chapter 9: Abnormal Labor and Intrapartum Fetal Surveillance Flashcards
Definition of labor and what causes abnormal labor
occurrence of uterine contractions of sufficient intensity, frequency, and duration to bring about demonstrable effacement and dilation of the cervix
i) Abnormal power (contractions), passenger, and passage lead to abnormal labor
Three ways to monitor the “power” of labor
Monitored by palpation, external tocodynnamometry or with intrauterine pressure catheters.
(1) Toco: External strain gauge that is placed on the maternal abdomen, recording frequency of uterine contractions
(2) IUPC: Same as above, in addition to the actual pressure generated by the uterine contractions
How much pressure do we need for proper cervical dilation and fetal descent?
For cervical dilation and fetal descent, you need 25 mmHg pressure with each contraction, with optimal being between 50-60 and at least 3 contractions in 10 minute intervals (not too fast or here won’t be adequate relaxation time for uteroplacental blood flow to baby to get oxygen)
Montevideo unit?
Montevideo unit: MVU: Number of contractions in 10 minutes * average intensity above the resting baseline IUP. Normal labor progress is around 200 MVU +
As for “passenger,” what do we look at for baby weight?
Weight greater than 4000-4500 grams = increased risk of dystocia (abnormal labor) and fetopelvic disproportion. US is great because it can estimate weight within 500-1000 grams near the end of term
5 typical malpresentations we associate with a larger baby:
(a) Asynclitism - Fetal head turned to one side
(b) Extension - Extended head
(c) Brow presentation (1/3000 births)
(d) Face presentation (1/600-1000 births) = C-Section
(e) Occipitoposterior - Longer labors (1 hour if experienced, 2 for new moms)
At what point during the first stage of labor do we call it “protracted”
In the latent phase. 20 hours or more in a nulliparous or 14 hours or more in a multiparous woman is considered protracted
In the active phase, a cervical dilation rate of less than 1cm/hour in a new mom or less than 1.2-1.5 cm/hr in a multiparous woman would be considered protracted
What point in the first stage of labor do we consider the labor arrested?
Latent phase can not arrest.
In active phase, if there is no cervical dilation for more than 2 hours, multiparous or not, you have arrest. If mom has regional anesthesia, we give her up to 4 hours before we call it arrest.
In the second stage of labor (i.e., cervical effacement 100% and baby is on the way out), what is considered a protracted vs arrested labor?
Protracted: With anesthesia, duration of more than 3 hours. Without anesthesia, greater than 2 hours or if fetus is descending at a rate of less than 1cm per hour.
Arrest: No descent after 1 hour of pushing.
What is augmentation?
Augmentation: Stimulation of uterine contractions when spontaneous contractions
have failed to result in progressive cervical dilation or descent of the fetus.
How do we augment?
- Amniotomy
- Oxytocin
What is an amniotomy? What do we need to be careful about
Artificial rupture of membranes that allows the fetal head instead of the amniotic sac to be the dilating force, and may stimulate release of prostaglandins to aid in augmenting the force of contractions
(a) Performed with a thin plastic rod with a sharp hook on the end
(b) SE: Drop in fetal heart rate due to cord compression,and an increased chance of chorioamnionitis. Evaluate FHR immediately pre and post procedure
How do we use oxytocin?
Oxytocin - Help get adequate contractions (3/10min) without going tachysystole (5/10min), unless this is what it takes to get the cervix to dilate. Uterine activity greater than 200 MVUs is also considered adequate
Can we do both amniotomy and oxytocin? When do we use these treatments?
Consider these treatments when frequency of contractions is less than 3 contractions per 10 minutes, intensity is less than 25 mmHg above baseline, or both.
(a) Doing both decreases labor by up to 2 hours but does not change the rate of Cesarean delivery
What do we do with a second stage delay?
Just because you have a prolonged second stage doesn’t mean baby is going to die. If FHR is ok and cephalopelvic disproportion has been ruled out, let nature take it’s slow course
What do we mean by operative vaginal delivery?
Forceps or vacuum
How often do we do operative vaginal delivery and what are the risks?
Risk of forceps and vacuum extraction (operative vaginal delivery) is intracranial hemorrhage. We only do operative vaginal delivery 10-15% of the time.
What 5 conditions are required to do operative vaginal delivery?
i) Scalp visible at introitus without separating labia
ii) Fetal skull has reached pelvic floor
iii) Sagittal suture is in anteroposterior diameter, right/left occiput anterior, or posterior position
iv) Fetal head is at or on the perineum
v) Rotation does not exceed 45 degrees
What is low operative vaginal delivery?
Low operative vaginal delivery – Application of forceps or vacuum when the leading point of the fetal skull is at station +2 or more and is not on the pelvic floor.
Two subtypes of low operative vaginal delivery
i) Rotation of 45 degrees or less (left or right occiput anterior to occiput anterior, or left or right occiput posterior to occiput posterior)
ii) Rotation greater than 45 degrees
Midpelvis operative vaginal delivery is what?
Application of forceps or vacuum when the fetal head is engaged but the leading point of the skull is above station +2
Indications (not requirements like the previous card) for operative vaginal delivery
No indication is absolute. Following apply when the fetal head is engaged and cervix is fully dilated
(1) Prolonged or arrested second stage of labor
(2) Suspicion of immediate or potential fetal compromise
(3) Shortening of the second stage for maternal benefit
Contraindications to operative vaginal delivery
No vacuum if baby
Forceps complications:
Perineal trauma, hematoma, pelvic floor injury to mom. Brain and spine, MSK injuries, and corneal abrasions for the baby. When weighing over 4000 grams, shoulder dystocia (fetus’ anterior shoulder becomes lodged against the pubic symphysis) risk increases
Risks of vacuum extraction
Risks: Less to mom. Less force than forceps, but intracranial hemorrhage, subgaleal hematomas, scalp lacerations, hyperbilirubinemia, and retinal hemorrhages are potential risks. Serious complications = 5% of time
Conditions associated with breech presentation
Premature birth, multiple pregnancies, polyhydramnios, hydrocephaly, anencephaly, aneuploidy, uterine anomalies, uterine tumors
Why exactly is breech presentation a bad thing?
Fetal anomalies could be present, prematurity is a risk, umbilical cord prolapse, and birth trauma
When do we do external cephalic version to move baby around if they are in breech or some other malpresentation
Performed after 36 weeks
(1) Because by then, if baby was gonna turn, it would have by now
(2) Less likely to revert back to breech at this point post-procedure
Risks of ECV
Premature ROM, placental abruption, cord accident, uterine rupture
When would we vaginally deliver a breech presentation baby?
You wouldn’t really. If you must, the baby needs to be more than 37 weeks along and be completey good to go otherwise.
Official requirements: Normal labor curve, gestational age >37 weeks, frank or complete breech presentation (due to risk of umbilical cord prolapse, vaginal delivery of a fetus in the footling position not recommended), absence of fetal anomalies on US, adequate maternal pelvis, fetal weight between 2,500 – 4000 grams, fetal head flexion (95% of time in breech, this is the case, but there are a 5% of cases with extension, in which case you need C-S to prevent head entrapment), adequate amniotic volume (3cm vertical pocket), and availability of anesthesia and neonatal support
Conditions associated with shoulder dystocia
Multiparity, postterm gestation, previous history of shoulder dystocia, and previous history of macrosomic birth.
What is turtle sign?
Turtle sign: Delivered fetal head may retract against maternal perineum
What is the McRoberts Maneuver and when do we do it?
McRoberts Maneuver: Hyperflexion of the mother’s legs tight to the abdomen.
(1) Done while applying suprapubic pressure to assist in dislodging the impacted shoulder
(2) Do not apply fundal pressure as this may result in uterine rupture and/or worsening shoulder impaction
What is the Zavanelli maneuver?
Zavanelli maneuver – Fetal head is flexed and reinserted into the vagina to re-establish umbilical cord blood flow and delivery via Cesarean section.
(1) More aggressive, and may be done while intentionally fracturing the fetal clavicle
How often does shoulder dystocia lead to brachial plexus injury?
Shoulder dystocia associated with 4 – 40% risk of brachial plexus injury, but fewer than 10% result in persistent brachial plexus injury
Responses by baby that indicate compromise to the uteroplacental unit
Initial responses include: Fetal hypoxia (decreased blood oxygen levels), shunting of blood flow to the fetal brain, heart and adrenal glands, and transient, repetitive, late decelerations of the FHR. If continued, anaerobic glycolysis will lead to metabolic acidosis)
Lactic acid accumulates and progressive organ damage ensues to heart and especially brain, possibly leading to permanent defects
What is neonatal encephalopathy?
Neonatal encephalopathy:
Difficulty initiating and maintaining respiration, depression of tone and reflexes, subnormal level of consciousness, and sometimes seizures seen in the earliest days of life in a term infant
Hypoxic-ischemic encephalopathy (HIE) is a subtype of neonatal encephalopathy in which there is limitation of blood flow and oxygen near the time of birth
Are NE’s caused by labor?
Approximately 70% of NE cases are due to factors present before the onset of labor
Essential criteria to define an acute intrapartum hypoxic event as sufficient to cause cerebral palsy
(a) Fetal metabolic acidosis
(i) Via umbilical cord arterial blood gas measurement (pH or equal to 12 mmol/L)
(b) Early onset or moderate neonatal encephalopathy in newborn of >=34 weeks of gestational age
(c) Spastic or dyskinetic cerebral palsy
(d) Exclusion of other identifiable causes (trauma, coagulopathy, infection, or genetic anomaly)
What is cerebral palsy?
Chronic disability of the central nervous system characterized by aberrant control of movement and posture appearing early in life and not as a result of progressive neurological disease
(i) Only one type, spastic quadriplegia, is associated with antepartum or intrapartum interruption of fetal blood supply
Two types of fetal heart monitoring
(a) External EFM: Doppler
(b) Internal EFM: Fetal electrode placed on presenting part of fetus
How do we measure baseline heart rate?
Baseline: Mean FHR rounded to nearest 5 bpm during a 10 minute period excluding periodic or episodic changes, marked variability, and segments that differ by more than 25 bpm. Must be for at least 2 minutes in a 10 minute
segment
(i) Normal: 110-160 bpm (Tachy>160, Brady
How do we measure baseline variability and what are the subtypes:
Measured from peak to trough in BPM
- Absent: No variability
- Minimal: Range detectable but fewer than 5 bpm
- Moderate (normal) – 6-25 bpm
- Marked: 25 bpm +
Why is variability in the baseline a good thing?
Decreased variability is associated with fetal hypoxia, academia, drugs that may depress the fetal CNS like maternal narcotic analgesia, fetal tachycardia, prolonged uterine contractions, prematurity, and fetal sleep
We want some variability. It’s a reassuring sign that reflects adequate fetal oxygenation and normal brain function
What is acceleration?
Visually apparent abrupt increase in the FHR with onset to peak in less than 30 seconds
What do we expect our accelerations to be?
(i) At 32 weeks +, defined as 15 bpm or more above baseline for 15 seconds or more but less than 2 minutes from onset to return
(ii)
Prolonged acceleration vs. baseline change
Prolonged acceleration: Lasts 2 minutes or more but less than 10 minutes in duration
Acceleration > 10 minutes is defined as a baseline change
Deceleration and what is a late decel
(i) Deceleration: Decrease from FHR associated with a uterine contraction, peaking in deceleration at the peak of contraction
(ii) Late = Lowest FHR after the contraction instead of before or during peak contraction
What is a sinusoidal pattern?
Visually apparent, smooth, sine wave-like undulating pattern in FHR baseline with a cycle frequency of 3-5 per minute which persists for 20 minutes or more
Late decels usually means:
Uteroplacental insufficiency
Early decels means:
Vagal nerve stimulation (from pushing, rapid labor, posterior fetal position, CPD)
Variable Decels means
Umbilical cord compression
Cat I FHR tracing means:
Normal. Predictive of normal fetal acid-base status at the time of observation, and may be followed in a routine manner, and no specific action is required.
CAT II Tracing means
Indeterminable. Not predictive of abnormal fetal acid-base status, yet do not have adequate evidence to classify as Category I or III. Continued surveillance and reevaluation is required
CAT III tracing means:
Abnormal. Predictive of abnormal fetal acid-base status at the time of observation. Requires prompt evaluation and efforts to resolve the abnormal FHR pattern, such as oxygen administration, change in maternal position, discontinuation of labor stimulation, and treatment of maternal hypotension
CAT I requirements:
Category I = Normal
(i) Baseline Rate 110 – 160 bpm
(ii) Baseline FHR variability: moderate
(iii) Late or variable decelerations: absent
(iv) Early decelerations: absent or present
(v) Accelerations: Present or absent
CAT II requirements:
Category II = Not Category I or III
(i) Bradycardia not accompanied by absent baseline variability
(ii) Tachycardia baseline rate
(iii) Minimal baseline variability
(iv) Absent baseline variability not accompanied by recurrent decelerations
(v) Marked baseline variability
(vi) Absence of induced accelerations after fetal stimulation
Cat III tracing requirements
Category III = No Bueno
(i) Absent baseline FHR variability along with any of the following:
1. Recurrent late decelerations
2. Recurrent variable decelerations
3. Bradycardia
(ii) Sinusoidal pattern
What can we do first if we get a non reassuring FHR tracing?
- Fetal stimulation
- Determine fetal blood pH or lactate
- Pulseoximetry
What algorithm do we follow if we have tried fetal stimulation and pulsox that aren’t working and/or have continued Cat II or Cat III tracings?
- Place patient in left lateral position
- Administer Oxygen
- Correct maternal hypotension
- Discontinue Oxytocin
- If these don’t work, consider tocolytic agents to stop contractions to prevent umbilical cord compression
- If Uterine tachysystole, use B-adrenergic drugs
- Amnioinfusion (infusion of fluid into amniotic cavity) can be used to relieve compression of umbilical cord in setting of oligohydramnios or when ROM has occurred
When do we stimulate the fetus and how can we do it?
Performed when an EFM tracing shows decreased or absent variability without spontaneous accelerations (in order to elicit one)
- Fetal scalp sampling
- Allis clamp scalp stimulation
- Digital scalp stimulation
- Vibroacoustic stimulation
First three involve direct access of fetal scalp through dilated cervix
b. 4 is through vibration through the abdomen near fetal head
c. If accelerations are noted after stimulation, then you have excluded acidosis. (3 and 4 are less invasive and are thus preferred.
d. Labor can continue when acceleration is noted
If fetal scalp scratching doesn’t wake the baby up, what is next?
If no response from stimulation, do scalp blood sample to check pH
What is meconium?
Thick black tarry substance found in the fetal instestinal tract
(a) Composed of amniotic fluid, lanugo (fine hair that covers the fetus), bile, fetal skin, and intestinal cells
When do we see meconium and why is it bad?
During fetal stress, fetus may pass this first stool in utero
(i) 10-20% of births, dark green or black amniotic fluid
(ii) Usually ok, but 6% of these fetus’ aspirate the meconium filled amniotic fluid, leading to meconium aspiration syndrome
1. Can lead to pneumonitis, pneumothorax, pulmonary artery hypertension
What do we do if we are suspecting meconium aspiration?
If you suspect meconium in the infant, intubate and suction before oxygenating, especially with a “non-vigorous” baby
