Fetal Heart Rate UTD

Question 1

What is the purpose of the 3-tier FHR classification system?

Answer 1

To standardize FHR interpretation and guide management based on fetal acidemia risk.

Question 2

What are the three FHR categories?

Answer 2

Category I (Normal), Category II (Indeterminate), Category III (Abnormal).

Question 3

What defines a Category I FHR pattern?

Answer 3

Baseline 110–160 bpm, moderate variability, no late or variable decelerations, early decels/accels may be present.

Question 4

What is the management for a Category I FHR tracing?

Answer 4

No resuscitation; continue monitoring. Intermittent auscultation acceptable in low-risk patients.

Question 5

What defines a Category III FHR pattern?

Answer 5

Absent variability AND recurrent late decels, recurrent variable decels, or bradycardia OR a sinusoidal pattern.

Question 6

What are the steps in managing Category III FHR?

Answer 6

Start in utero resuscitation, perform scalp stimulation, prepare for expedited delivery.

Question 7

What is the role of scalp stimulation in Category III?

Answer 7

If it induces acceleration, fetal pH <7.20 is unlikely. No accel suggests acidemia.

Question 8

What are the key in utero resuscitation methods?

Answer 8

Maternal repositioning, IV fluids, stop oxytocin, tocolytics (terbutaline), stop pushing, nitroglycerin.

Question 9

When is oxygen indicated in FHR management?

Answer 9

Only in maternal hypoxemia; not effective for fetal resuscitation if mother is normoxic.

Question 10

What defines a Category II FHR pattern?

Answer 10

Any FHR pattern not meeting criteria for Category I or III.

Question 11

How is Category II generally managed?

Answer 11

Continuous monitoring, scalp stimulation, resuscitation, frequent reassessment.

Question 12

What is the significance of moderate variability in Category II?

Answer 12

Strongly associated with absence of fetal acidosis.

Question 13

How are recurrent late decels with moderate variability managed?

Answer 13

Continue monitoring, correct underlying causes like tachysystole or hypotension.

Question 14

What are causes of fetal tachycardia?

Answer 14

Infection, medications (e.g., beta-agonists), hyperthyroidism, hypoxia, abruption.

Question 15

How is fetal tachycardia managed?

Answer 15

Treat underlying cause; deliver if acidemia or abruption suspected.

Question 16

What causes variable decelerations?

Answer 16

Cord compression due to oligohydramnios, nuchal cord, prolapse.

Question 17

What is the role of amnioinfusion?

Answer 17

Used in recurrent variable decels; reduces cesareans and improves outcomes.

Question 18

What causes minimal/absent variability without decels?

Answer 18

Fetal sleep, CNS depressants, hypoxemia, corticosteroids.

Question 19

How is new-onset minimal variability managed?

Answer 19

Scalp stimulation; presume sleep cycle if short. Delivery if tracing doesn’t improve.

Question 20

What are causes of prolonged decels or bradycardia?

Answer 20

Cord prolapse, abruption, uterine rupture, hypotension, tachysystole.

Question 21

What is the management of prolonged deceleration?

Answer 21

Treat underlying cause; expedite delivery if unresolved.

Question 22

What is the prevalence of Category I during labor?

Answer 22

78% overall, 61% in final 2 hours.

Question 23

What is the prevalence of Category II during labor?

Answer 23

22% overall, 39% in final 2 hours.

Question 24

What is the prevalence of Category III during labor?

Answer 24

0.004% overall, 0.006% in final 2 hours.

Question 25

Explain the physiologic mechanism behind late decelerations during uterine contractions.

Answer 25

Late decelerations are caused by transient fetal hypoxemia. Uterine contractions reduce uteroplacental blood flow, stimulating fetal chemoreceptors. This triggers sympathetic vasoconstriction and baroreceptor-mediated vagal slowing of the heart rate after the contraction begins.

Question 26

Why is gestational age important when interpreting fetal heart rate accelerations?

Answer 26

As gestational age advances, the autonomic nervous system matures. Before 32 weeks, accelerations of 10 bpm for 10 seconds are expected, while after 32 weeks, accelerations should be ≥15 bpm for ≥15 seconds. Reactivity improves with maturation.

Question 27

Compare and contrast the typical causes of early, variable, and late decelerations.

Answer 27

Early: fetal head compression (benign). Variable: cord compression. Late: uteroplacental insufficiency (hypoxia).

Question 28

What defines a reactive nonstress test (NST) after 32 weeks, and what does it indicate?

Answer 28

Two or more accelerations of ≥15 bpm lasting ≥15 seconds in 20 minutes. It indicates adequate fetal oxygenation and neurologic integrity.

Question 29

What is the significance of a nonreactive NST, and how is it managed?

Answer 29

It may suggest fetal hypoxia or non-pathologic causes (e.g., sleep cycle, medications). It requires at least 40 minutes of monitoring. Further evaluation includes vibroacoustic stimulation, repeating the test, or performing a BPP or CST.

Question 30

Why are false-positive NSTs common, and what are their clinical implications?

Answer 30

Up to 60% of nonreactive NSTs result in intervention without confirming fetal compromise. This leads to unnecessary interventions and highlights the need for secondary testing.

Question 31

How does vibroacoustic stimulation affect NST performance and outcomes?

Answer 31

It shortens testing time and reduces nonreactive results by stimulating fetal movement. It's safe and effective but lacks standardized protocols.

Question 32

Describe the interpretation criteria for a contraction stress test (CST).

Answer 32

Positive: late decels with ≥50% contractions. Negative: no late or significant variable decels. Equivocal: intermittent late or tachysystolic. Unsatisfactory: <3 contractions in 10 min or uninterpretable.

Question 33

What makes CST less commonly used than NST in clinical practice?

Answer 33

CST is more invasive, time-consuming, and has contraindications like placenta previa or prior uterine surgery. NST is noninvasive and easier to perform.

Question 34

How can maternal conditions affect the interpretation of NST and CST?

Answer 34

Conditions like hypotension, medication use, or smoking can alter FHR patterns and must be considered to avoid misinterpretation.

Question 35

What is the significance of accelerations during a positive CST?

Answer 35

Presence of accelerations may indicate a lower risk despite decelerations, possibly reducing the need for delivery. Still, further evaluation is warranted.

Question 36

Discuss the role and limitations of NST and CST based on evidence from clinical trials.

Answer 36

RCTs show limited benefit in reducing perinatal morbidity or mortality. Many tests have high false-positive rates. Computerized analysis may improve outcomes, but older trials limit interpretation.