Baseline & variability
This is the normal fetal heart rate baseline range.
What is 110-160 bpm?
This physiologic mechanism is responsible for early decelerations, and is not associated with fetal acidemia.
What is fetal head compression causing a vagal reflex?
ACOG: Early decels = benign; no correlation with acidemia.
NICHD definitions (1997 & 2008): via increased intracranial pressure → vagal stimulation → drop in HR.
This precise definition of tachysystole must be used regardless of fetal heart tracing category
What is >5 contractions in 10 minutes averaged over 30 minutes?
A tracing with baseline 110–160, moderate variability, and no late/variable decelerations is classified as this.
What is category I.
• Early decelerations: present or absent
• Accelerations: present or absent
This simple bedside maneuver is usually the first step in treating many nonreassuring FHR patterns.
What is maternal repositioning?
A fetal baseline above 160 bpm is called this, and can be caused by maternal fever, infection, or dehydration.
What is fetal tachycardia?
This finding differentiates a prolonged deceleration from a baseline change.
What is duration >2 minutes but <10 minutes?
NICHD: 2–10 minutes = prolonged deceleration; ≥10 minutes = baseline shift (bradycardia).
This quantitative measure, expressed in Montevideo units (MVUs), defines adequate labor per IUPC.
What is ≥200 MVUs over 10 minutes?
Friedman curve; confirmed by later labor progress studies.
SMFM: adequate power = ≥200 MVUs for active labor.
Absent variability plus recurrent late decelerations is this Category.
What is Category III?
• Absent baseline FHR variability and any of the following:
• Recurrent late decels
• Recurrent variable decels
• Bradycardia
• Sinusoidal pattern
This intervention reduces recurrent variable decelerations by relieving cord compression after ROM.
This is the minimum number of minutes of identifiable baseline needed within a 10-minute window to define baseline fetal heart rate.
What is at least two minutes?
This deceleration pattern, often seen after epidural placement, is related to maternal hemodynamic changes rather than fetal pathology.
What is a prolonged deceleration caused by maternal hypotension?
Up to 10–15% incidence after epidural.
Supported by anesthesia literature and ACOG guidelines.
Improves with maternal repositioning and fluids.
This intervention is first-line for recurrent variable decelerations associated with tachysystole even before considering amnioinfusion.
What is reducing or stopping oxytocin?
Oxytocin is most common iatrogenic cause of tachysystole.
A Category II tracing with minimal variability but no recurrent decelerations should be managed initially with these supportive steps
What are intrauterine resuscitation measures (repositioning, fluids, stop oxytocin)?
Name at least three “intrauterine resuscitation” steps should be taken for Category II tracings.
What are repositioning, IV fluids, reducing/ stopping oxytocin, oxygen (strong evidence against oxygen in the absence of maternal hypoxia ), and treating tachysystole?
This physiologic mechanism is the primary driver of fetal heart rate variability.
What is the interplay between sympathetic and parasympathetic (vagal) nervous systems?
Variability reflects neurologic integrity, fetal oxygenation, and autonomic balance.
See ACOG Practice Bulletin 106
This key distinction between variable and late decelerations explains why variables improve with amnioinfusion, but lates do not.
What is the underlying cause (cord compression vs uteroplacental insufficiency)?
Multiple RCTs: amnioinfusion reduces variable decels but no effect on lates.
This physiologic mechanism explains why tachysystole increases the risk for fetal acidemia.
What is reduced intervillous blood flow during shortened relaxation time?
Uterine contraction → transient ↓ uteroplacental perfusion.
Without rest periods → cumulative fetal hypoxemia.
ACOG: tachysystole = risk for fetal compromise.
Name two situations in which Category III tracings warrant immediate consideration of delivery.
What are persistent bradycardia OR absent variability with recurrent decels despite resuscitation?
When Category III patterns persist despite resuscitation, the next step is this.
What is expedited delivery (operative vaginal or C-section)?
Meta-analyses show this FHR characteristic has the highest negative predictive value for acidemia ( > 95%).
What is moderate variability?
Moderate variability is the best indicator of normal acid-base status. On FHT, moderate variability is 6-25 bpm fluctuation in fetal heart rate from beat to beat, and excludes decelerations and accelerations.
Absent: amplitude range undetectable
Minimal: amplitude range ≤ 5 bpm
Marked: > 25 bpm
This advanced physiologic explanation describes why late decelerations occur during uteroplacental insufficiency.
What is chemoreceptor-mediated reflex bradycardia triggered by transient fetal hypoxia during uterine contraction peaks?
Uterine contraction → ↓ uteroplacental perfusion → ↓ fetal pO₂ → carotid chemoreceptors → vagal response
Fetus will also peripherally vasoconstrict in response to low oxygen and will prioritize blood flow to vital organs
This drug is commonly used for acute tocolysis in tachysystole, given as 0.25 mg SQ.
What is terbutaline?
• Beta-agonists reduce uterine contractions and improve fetoplacental oxygen delivery
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
•Cat III
This intervention is recommended by ACOG when a Category II tracing includes recurrent late decelerations without tachysystole, and is supported by data showing reduction in late decel frequency and improved fetal pH.
What is a maternal IV fluid bolus (up to 1 L isotonic crystalloid)?
• Increased maternal intravascular volume improves uteroplacental perfusion; studies show transient improvement in FHR and umbilical arterial pH.