Fetal Well-Being in Labor

Question 1

Define: baseline fetal heart rate

Answer 1

• Mean FHR rounded to increments of 5 bpm during a 10-minute segment
• Excluding:
  
  • Periodic or episodic changes
  • Periods of marked variability
  • Segments of baseline that differ by > 25 bpm.
• Duration must be ≥ 2 minutes.

Question 2

Define: variability

(name types)

Answer 2

• Fluctuations in the baseline FHR ≥ 2 cycles/min
• Absent variability – amplitude range undetectable
  • Without decels may be idiopathic and not associated with acidemia
• Minimal variability – amplitude visually detectable but < 5 bpm
  
  • If no decels - not associated with acidemia
  • Rest cycles - typically last 20 to 40 min but sometimes as long as 75 to 80 min
• Moderate variability – amplitude range from 6 – 25 bpm
• Marked variability – amplitude > 25 bpm
  
  • May be a response to short period of hypoxia but generally not assiciated with poor outcome

Question 3

Define: bradycardia

Answer 3

• Baseline rate < 110 bpm
• Rate < 60 bpm = emergency
  
  • Fetus unable to increase SV to sustain adequate circulation through the heart and coronary arteries
• Both asphyxial and non-asphyxial causes possible
  
  • Non-asphyxial causes:
    
    • Fetal heart block
    • Maternal hypothermia
    • Mild bradycardia in the 100–120 bpm range can be idiopathic in the postmature fetus
    • Rapid descent of presenting part or at the end of 2nd stage: when fetal head compression → increased ICP → vagal response
      
      • Cerebral oxygenation at FHR > 80 bpm and variability retained.
    • Administration of intrathecal opioids or local anesthetics for epidural analgesia.
      
      • Maternal hypotension, s/t sympathetic block → decrease in uteroplacental blood flow.
      • Transient bradycardias or prolonged decelerations usually retain normal variability, rarely associated with adverse outcomes.
  • Asphyxial causes:
    
    • Acute emergency events such as prolapsed cord, placental abruption, uterine rupture, or vasa previa
• Bradycardia accompanied by moderate variability not associated w/ fetal acidemia (no intervention required)

Question 4

Define: tachycardia

Answer 4

• Baseline rate > 160 bpm
• Tachycardia alone not usually associated with poor outcomes in the term fetus.
• Short periods of tachycardia are a normal compensatory response to transient hypoxemia.
• Sustained tachycardia in a term fetus may be caused by developing acidemia, maternal or fetal infection, cardiac arrhythmia, or it may be idiopathic.
  
  • Other causes include administration of beta-mimetic drugs or ephedrine given to correct maternal hypotension.
  • More rarely, fetal tachycardia occurs secondary to fetal anemia (Rh isoimmunization), acute fetal blood loss (placental abruption), an abnormal fetal conduction system (fetal arrhythmia), or poorly controlled maternal hyperthyroidism.
• Sustained tachycardia, especially if accompanied by minimal variability and recurrent decelerations, may indicate that the fetus’s ability to compensate for repeated hypoxia is limited.
  
  • May appear after recurrent decelerations present for some period of time but before a terminal bradycardia becomes evident
  • Characteristic of FHR pattern evolution when acidemia is increasing

Question 5

Define: acceleration

Answer 5

• Visually apparent abrupt increase (onset to peak < 30 seconds) of FHR above baseline.
• Peak ≥ 15 bpm.
• Duration ≥ 15 bpm and < 2 minutes.
• ***GA < 32 weeks***
  
  • Peak ≥ 10 bpm above baseline
  • Duration ≥ 10 seconds is an acceleration

Question 6

Early deceleration

• Define
• Significance
• Physiological basis
• Possible causes
• Appropriate treatment

Answer 6

* Define:

* Visually apparent gradual decrease (≥ 30 seconds to nadir) of FHR below baseline.
* Return to baseline associated with a uterine contraction.
* Nadir occurs at the same time as the peak of the contraction.
    * Onset/nadir/recovery of decel mirror contraction * Baroreceptor mediated * Mechanism unknown - thought to be head compression * Benign, no treatment needed

Question 7

Late deceleration

• Define
• Significance
• Physiological basis
• Possible causes
• Appropriate treatment

Answer 7

• Define:
  
  • Visually apparent gradual decrease (≥ 30 secs to nadir) of FHR below baseline.
  • Return to baseline associated with a uterine contraction.
  • Nadir occurs after the peak of the contraction.
  • Generally, onset/nadir/recovery of the decel occur after the onset/peak/recovery of the contraction
• Physiology:
  
  • Contraction → decrease in uteroplacental perfusion → lower O2 levels in fetal circulation
  • Hypoxemia detected by chemoreceptors in carotid artery, carotid sinus, and aortic arch.→ vagally mediated drop in FHR (alpha adrenergic response in endothelium of blood vessel → central HTN → baroreceptor → decreased FHR)
    
    • Chemoreceptor stimulation takes time (deoxygenated blood must first traverse UV before reaching the chemoreceptors) → hence the “late” decel
• Possible causes:
  
  • Uteroplacental insufficiency
• Significance
  
  • Late decel + moderate variability → physiologic response to transient hypoxemia, rather than an indicator of the presence of acidemia.
  • Recurrent late decels + minimal or absent variability → most commonly associated with fetal acidemia
• Appropriate treatment:
  
  • Delivery if Cat III or concern for developing acidemia

Question 8

Variable deceleration

• Define
• Significance
• Physiological basis
• Possible causes
• Appropriate treatment

Answer 8

# * Define
    * Visually apparent abrupt decrease (\< 30 secs to nadir) in FHR below baseline.

* Decrease ≥ 15 bpm below baseline.
* Duration ≥ 15 seconds and \< 2 minutes from onset to return to baseline.

• Possible causes
  
  • Cord around neck/body, true knots, frank and occult prolapse of the cord, and compression due to decreased amniotic fluid
• Physiological basis
  
  • Baroreceptor mediated
  • Cord compression
    
    • UV compressed → decreased preload → less blood to baby → spike (shoulder) in HR
    • Compression intensifies → UA compression → decreased afterload → vagal mediated HR decel
• Significance
  
  • If return to baseline < 60 seconds with concomitant normal baseline and moderate variability - not associated with fetal acidemia.
  • Recurrent variable decelerations with minimal or absent variability - associated with fetal acidemia and require urgent evaluation and consideration of intervention
  • Loss of “shoulder” → often see longer variables
    with slower recovery
• Appropriate treatment

Question 9

Sinusoidal pattern

• Define
• Significance
• Physiological basis
• Possible causes
• Appropriate treatment

Answer 9

• Define
  
  • True sinusoidal extremely rare
  • Absence of short-term variability
  • Undulation occurs at a rate of 2 to 6 cycles per minute
  • Undulating, recurrent uniform FHR equally distributed 5 to 15 bpm above/below baseline
• Significance
  
  • Always an ominous sign → immediate intervention is indicated.
  • May also appear shortly before death in a severely asphyxiated fetus
• Physiological basis
  
  • Brainstem malfunction?
• Possible causes
  
  • Clinically significant anemia (maternal-fetal hemorrhage following vasa previa, uterine rupture, or abruption, Rh isoimmunization)
• Appropriate treatment
  
  • Notify the consulting physician ASAP
  • Prepare patient for emergency C/S
  • Notify NICU to prepare for a potentially anemic or hypovolemic newborn.

Question 10

Define: pseudosinusoidal pattern

Answer 10

• Not an NICHD-recognized FHR pattern because it is commonly the result of opioid administration, rather than being an intrinsic FHR characteristic.
• Clinically insignificant pattern
• Intermittent and bracketed by periods of moderate variability.
• Differs from a real sinusoidal pattern in 2 ways:
  
  1. Variability is retained
  2. > 2 to 6 cycles per minute.

Question 11

Define: cardiac arrhythmias

Answer 11

• ~ 1% to 3% of term fetus
• ~ 90% of fetal arrhythmias are transient/benign
• Consulting physician should evaluate any fetus with an arrhythmia, and a plan should be made for ongoing collaboration as long as the arrhythmia is present.
• Can be heard on audible Doppler devices and can be seen on FHR tracings, but cannot be accurately diagnosed via EFM.
• Neonatal/pediatric attendance at birth may be recommended depending on the rate and persistence of the arrhythmia.

Question 12

Define: tachysystole

Answer 12

• 5 contractions in 10 minutes averaged over a 30-minute window
• Can affect fetal gas exchange

Question 13

Contractions intensity (nose/chin/forhead and corresponding pressures

Answer 13

Contraction intensity by palpation (fingertip can usually detect IUP >20 mg Hg:

Mild – nose (< 40 mmHg via IUPC)

Moderate – chin (40 – 70 mmgHg via IUPC)

Strong – forehead (> 70 mmHg via IUPC)

Question 14

Define: uterine resting tone

Answer 14

Should be < 30 mmHg

Question 15

Category I FHR Tracing

NICHD Criteria

Answer 15

• Baseline rate: 110–160 bpm
• Baseline FHR variability: moderate
• Late or variable decelerations: absent
• Early decelerations: present or absent
• Accelerations: present or absent

Question 16

Category II FHR Tracing

NICHD Criteria

Answer 16

All FHR tracings not categorized as Category I or Category III. Includes any of these patterns:

• Baseline rate:
  
  • Bradycardia not accompanied by absent baseline variability
  • Tachycardia
• Baseline FHR variability:
  
  • Absent (without recurrent decels)
  • Minimal, or Marked
• Accelerations:
  
  • Absence of induced accelerations after fetal stimulations
• Periodic or episodic decelerations:
  
  • Recurrent variable decelerations accompanied by minimal or moderate baseline variability
  • Prolonged deceleration > 2 minutes but < 10 minutes
  • Recurrent late decelerations with moderate baseline variability
  • Variable decelerations with other characteristics, such as slow return to baseline, “overshoots,” or “shoulders”

Question 17

Category III FHR Tracing

NICHD Criteria

Answer 17

Absent baseline FHR variability and any of the following:

• Recurrent late decelerations
• Recurrent variable decelerations
• Bradycardia
• Sinusoidal pattern

Question 18

How often does a high-risk patient need FHR during:

First stage (active)

and

Second stage

Answer 18

First stage: q 15 minutes

Second stage: q 5 minutes

Question 19

How often does a low-risk patient need FHR during:

First stage (active)

and

Second stage

Answer 19

First stage: q 30 minutes

Second stage: q 15 minutes

Question 20

Intermittent auscultation

• Define
• Technique
• Accuracy
• Advantages
• Disadvantages
• Indications

Answer 20

• Done with Doppler, pinard, or fetoscope
• Technique:
  
  • Listen for 60 seconds initially between contractions to establish a baseline (and HR regularity) several times within a 10 minute period
  • Multicount strategy (more reliable than single count)
    
    • Counts FHR for a period of 6, 10, or 15 seconds several times over the course of the listening period.
    • Rest period of 5 or 10 seconds between each count.
    • Each count is then multiplied by the appropriate number to obtain an FHR-per-minute rate.
  • Listen for accels (not necessary for Cat I but reassuring of fetal wellbeing)
  • Listen for decels starting at peak of contraction and for 30 - 60 secs after using multicount strategy
    
    • If a decel is heard, listen through successive contractions or several contractions in a 10-minute window to determine recurrent vs nonrecurrent.
• Listen q 15 - 30 min 1st stage, q 5 - 15 min 2nd stage
• Advantages:
  
  • Supports physiologic birth/shared decision making
• Disadvantages:
  
  • Requires one-to-one continuous care
  • May not be technically feasible for women who have high BMIs or in certain positions such as hands and knees
  • Does not detect variability
  • Can miss significant decels if technique isn’t accurate
  • May be hard to determine baseline
• Indications: low risk patients

Question 21

External fetal monitoring

• Define
• Technique
• Accuracy
• Advantages
• Disadvantages
• Indications

Answer 21

• Define
  
  • Doppler device that has a transducer and a receiver is secured onto the maternal abdomen, over the area of the fetal heart
  • Counts interval between fetal heartbeats, calculates bpm rate, and plots rate on graph paper → individual plot points merge into a jagged line
    • Time interval between each heart beat typically varies secondary to vagus input
    • Reflects CNS function and well-being
• Accuracy
  
  • Not more accurate than IA in predicting poor outcomes in low risk patients
• Advantages
  
  • Can assess baseline, variability, differentiates type of decels (early/variable/late)
  • May detect prescence of arrhythmia (tho can’t dx type)
• Disadvantages
  
  • Limits movement to bed or near bed
  • With central monitoring may not have nurse in room as labor support
  • May be difficult to pick up signal in patients with high BMI
  • Could potentally pick up parent’s HR instead
• Indications: basically anyone who isn’t low risk

Question 22

Internal fetal monitoring

• Define
• Technique
• Accuracy
• Advantages
• Disadvantages
• Indications

Answer 22

• Define
  
  • Fetal scalp electrode (FSE) placed a few millimeters into the fetal scalp and transmits the fetal EKG to the monitor
• Indications:
  
  • FHR or contractions need to be monitored continuously and an adequate tracing is not available via external monitoring (ie high BMI)
• Accuracy
  
  • Not more accurate than EFM (that is reading well)
• Advantages
  
  • Consistent readout of FHR in patient difficult to pick up EFM
  • Will not pick up parent HR
• Disadvantages
  
  • Requires ROM and cervical dilation of 1 - 2 cm
  • Contraindicated if parent has disease with concern for vertical transmission (ie HIV, hepatitis, active herpes)
  • Contraindicated if fetus has coagulation disorder, if presentation is unknown or a face presentation
• Potential adverse events:
  
  • Scalp laceration
  • Localized infection, and (rarely) abscess.
  • Facial injury or insertion in the eye or ear when FSE is placed without accurate diagnosis of fetal position

Question 23

Uterine activity monitoring

(External palpation, external toco, internal uterine activity monitoring)

• Define
• Technique
• Accuracy
• Advantages
• Disadvantages
• Indications

Answer 23

• Maternal perception varies individually, but generally at 15 mmHg (pressure required to distend the lower uterine segment and create pressure on the cervix)
• Manual palpation: generally preceivable at 10 mmHg
• External tocodynamometer (toco) - placed on fundus and secured with a belt that goes around abdomen
  
  • Records changes in pressure when fundus tightens during a contraction
  • Records contraction duration and frequency, does not record intensity accurately
  • Tightening straps or changing toco position can cause the device to show a very different apparent intensity of contractions.
• Internal uterine monitoring - place intrauterine pressure catheter (IUPC) through the cervix into uterine cavity.
• Advantage:
  
  • Specific info about resting tone, actual pressure generated by contractions, and accurate timing of onset, peak, and completion of a contraction.
  • IUPC may be used for quantitative measurement of uterine contraction intensity in Montevideo units (MVU)
    
    • Add together the peak pressures of all contractions in a 10-minute window.
    • Adquate for natural progression of labor: MVU ~ approximately 200 when subtracting baseline tone, or 240 when the baseline tone included
  • Can perform amnioinfusion through IUPC
• Disadvantages:
  
  • Increased risk of infection if the IUPC is left in place for an extended period of time
  • Laboring patient is bedbound

Question 24

Describe normal cord blood gases

Answer 24

Want pH > 7 and BE < - 10

Question 25

Describe abnormal cord blood gases as they correlate to respiratory and metabolic acidosis

Answer 25

Respiratory • pH \<7.25 * pO2 variable * pCO2 \>50 mmHg * BE \< -10 mEq/liter Metabolic • pH \<7.25 * pO2 \<20 mmHg * pCO2 45-55 mmHg * BE \> -10mEq/Liter

Question 26

Describe the correct method for cord blood collection for gases

Answer 26

* Collecting a sample of UA blood and then a sample of UV blood in a heparinized syringe from a section of umbilical cord that has been clamped at both ends. * Fetal vessels on the surface of the placenta may be used if a length of umbilical cord is not available. * Blood gases in UA - status of the fetus * Blood gases in UV - status of the intervillous space * Both UA and UV samples needed so results can be correctly interpreted. When only one sample is obtained or when the samples yield the same results, one cannot be certain if the values are from the UA or the UV. * Should be obtained when a concern arises that the fetus might have experienced clinically significant acidemia. There are no standard guidelines that recommend indications for umbilical cord blood gas analysis.

Question 27

Factors which can improve or impede optimal placental perfusion:

Answer 27

* Very little can be done physiologically to increase uterine blood flow if it is needed. * Use of side-lying positions to prevent compression of the inferior vena cava * May need to change position to relieve cord compression as well * Administration of tocolytics that stop uterine contractions for a short time

Question 28

Umbilical and uterine blood flow

Answer 28

* Uterine spiral arteries become deinnervated during pregnancy as their endothelial linings are replaced with trophoblastic tissue → arteries become maximally → facilitate blood flow into the intervillous space * Arteries lose their ability to constrict if pressure in the vessel drops * Exchange of nutrients and gases occurs with the fetal blood as the maternal blood flows around the branch villi. * Two umbilical arteries carry poorly oxygenated fetal blood to the placenta * One umbilical vein carries oxygenated blood to the fetus. * Placental cotyledons are separated from each other by septa projections of the decidua basalis. Each cotyledon consists of two or more main stem villi and branches.

Question 29

Physiology of placental function in gas exchange

Answer 29

* Fetal respiration depends on: * Adequate maternal blood flow into the intervillous space * Sufficient functional placental villi for gas exchange * Adequate diffusion, facilitated diffusion, and active transport of gases, nutrients, and fetal waste products * Unimpaired fetal circulation through the placenta and umbilical cord. * Fetus can use aerobic or anaerobic metabolism to produce the energy needed for growth and metabolic processes: * Aerobic: pyruvate → CO2 and H2O * CO2 easily diffuses across placenta * Anaerobic: pyruvate → ATP + lactic acid (C3H6O3) * Lactic acid does not cross placenta easily → metabilic acidosis

Question 30

Physiology of fetal heart rate regulation

Answer 30

Controlled by: * Sympathetic * Parasympathetic * Chemoreceptor * Baroreceptor * Central nervous system (CNS)

Question 31

Physiology of the fetal heart: Sympathetic and parasympathetic nervous system

Answer 31

* Sympathetic fibers that innervate the myocardium respond to catecholamine stimulation by increasing the FHR. * 2nd tri: PNS matures → parasympathetic input (mediated by vagus nerve) becomes dominant over sympathetic stimulation → baseline heart rate gradually slows. * Sinoatrial node (right atrium), has highest intrinsic rate → pace for the fetal heart beats. * Vagus nerve originates in the medulla oblongata and terminates in the SA node of the fetal heart, * Vagal stimulation changes the FHR by causing the interval between successive beats to vary

Question 32

Physiology of the fetal heart: chemoreceptors and baroreceptors

Answer 32

* Chemoreceptors found in the aortic arch and CNS are sensitive to changes in O2 and CO2 in blood * Increased CO2 → chemoreceptors signal the medulla oblongata → stimulates the vagus nerve → slows FHR. * Baroreceptors in the aortic and carotic arches rapidly detect changes in BP. BP rises → quick reflex (via vagal nerve) to slow FHR

Question 33

Difference between acidemia and acidosis?

Answer 33

Increased concentration of hydrogen ions in the: * Acidemia - blood (like anemia) * Acidosis - tissues

Question 34

What is base excess?

Answer 34

* Amount of base (substance able to accept H+ ions, primarily HCO3) that is available for buffering hydrogen ions. * As metabolic acidosis increases, the base excess decreases

Question 35

The effect of maternal hormones (catecholamines), BP, HR, and temp on the FHR

Answer 35

* Hormones = sympathetic fibers respond to catecholamines by increasing the FHR (though persistent/long term catecholamine floods will result in hypoxia d/t decreased placental perfusion) * Hypotension → fetal bradycardia * Hypertension → decrease blood flow to fetus * Maternal HR = intervention for tachycardia depends on the cause. * Fever- antipyretics + hydration * O2 - 100% O2 at 8-10L/min * Can give meds: digoxin, calcium channel blockers (nifedipine), beta-blockers (propranolol/inderal), antiarrhythmic (procainamide, quinidine → cross to fetus to slow FHR too) * Maternal fever = most common cause of fetal tachycardia

Question 36

Describe the relationship between meconium and gestational age

Answer 36

* 10-15% of all births * Occurs mainly after 37 weeks (stress) * generally not before 34 weeks * After 40 weeks (normal physiologic response to peristalsis) * Expect to see it after 41 weeks (sufficient stool in bowel to make baby pass it) * \*\*\*Must document heart rate * More significant in the presence of an abnormal FHR tracing * More significant when present in early labor, and early gestation

Question 37

Describe the different colors and consistency of meconium stained fluid, membranes and placenta, and the corresponding significance of each

Answer 37

* Fresh meconium - dark, green-brown * Progresses from greenish-tan to muddy brown to light tan (6 - 10 hours) * Stains membranes: more than several hours * May become barely noticeable over time: happened a couple of days ago * Document consistency (thin, thick, particulate) and amount passed (but may be "hiding" behind baby)

Question 38

Describe the potential etiologies of meconium passage

Answer 38

* Physiologic maturational event due to increased peristalsis * Hypoxia (vagal response from head/cord compression causes sphincter relaxation) * Acute chorioamnionitis

Question 39

Describe the risk to the newborn of meconium aspiration

Answer 39

* Pneumonitis * Hypoxia * Respiratory failure * Persistent pulmonary hypertension * May need ventilator or in worse case ECMO

Question 40

Describe management strategies for the fetus and newborn with meconium in labor

Answer 40

* None needed if FHR tracing is reassuring and labor progressing normally * If thick meconium and laboring outside hospital → consider transfer