Podcast Summary

Dr. Chapa’s OBGYN Clinical Pearls

Episode: FHT Baseline Change (110-160) in Labor: Danger, or Disregard?
Date: December 27, 2025
Host: Dr. Chapa

Episode Overview

This episode addresses an insightful listener question:
Is a change in fetal heart rate (FHT) baseline within the normal range (110–160 bpm) during labor something to worry about, or can it be safely disregarded? Dr. Chapa reviews evidence and clinical guidelines to unpack what’s normal, what should raise concern, and clarifies the distinction between baseline shifts and concerning “zigzag”/wandering patterns in FHT tracings. The discussion is clinically focused, interactive, and designed to clarify key nuances for obstetric providers and trainees.

Key Discussion Points and Insights

1. Three-Tier FHT Classification Refresher

(Timestamp: 00:31–02:50)

• Category 1: Normal
  • Baseline 110–160 bpm, moderate variability, accelerations may/may not be present, no concerning decelerations.
• Category 2: Indeterminate
  • Includes tachycardia/bradycardia with normal variability; requires continued surveillance.
• Category 3: Abnormal
  • Immediate action required, often defined by absent variability with recurrent decelerations or bradycardia.

2. Listener's Clinical Question

(Timestamp: 01:20–03:50)

• Scenario: Baseline FHT starts at 120, later shifts to 150 bpm (still within normal), with normal variability. Is this dangerous?
• Two parts:
  • Is a baseline shift upwards (reverses also possible) within normal bands concerning?
  • What is the difference between this and a zigzag (wandering) baseline?

"If there's a change in baseline but still within the normal levels…what do you do?" — Dr. Chapa, 02:05

3. When is a Change in Baseline Okay?

(Timestamp: 05:15–15:50)

• Definition of FHT Baseline: Average heart rate over >10 minutes.
• Normal for baseline to shift during labor, provided:
  • Remains 110–160 bpm
  • Variability is moderate/intact
  • N o repetitive, pathological decelerations or clinical markers of distress
• Notable Evidence:
  • Up to 42–50% of term labors exhibit baseline shifts within normal range without neonatal morbidity.
    • AJ Perinatology, 2017; AJOG, 2023
• Such shifts commonly reflect physiologic catecholamine stress, NOT concerning pathology alone, unless other findings are present.

"If there's nothing else going on...and the heart rate just changes between 110 to 150, if it doesn't cross the threshold of tachycardia, yes, that is absolutely normal." — Dr. Chapa, 10:45

• Once FHT crosses 160 bpm (tachycardia), further workup is warranted (e.g., infection, medications, maternal fever).

4. What About Maternal Infection (IAI) and Fetal Tachycardia?

(Timestamp: 08:00–09:30, 13:45–14:45)

• Fetal tachycardia (≥160 bpm) is a classic sign of possible intra-amniotic infection (IAI), even without maternal fever.
  • Other IAI signs: uterine tenderness, foul-smelling amniotic fluid, maternal leukocytosis
• But: Baseline changes below 160 without other clinical signs do NOT equate to IAI.

"You do not need fever to be present to diagnose IAI if there is fetal tachycardia." — Dr. Chapa, 09:15

5. Zigzag/Wandering FHT Baseline: A True Red Flag

(Timestamp: 18:00–21:30)

• Wandering/zigzag baseline:
  • Baseline fluctuates up and down in plateaus over 10-minute segments, often with decreased, minimal, or absent variability.
  • Associated with autonomic instability; often follows recurrent decelerations.
  • Implies potential fetal hypoxia, requires close surveillance/intervention.
• Key difference:
  • Zigzag = instability
  • Sustained new baseline (even if higher/lower but stable, with normal variability) = physiologic.

"If it keeps wandering, zigzagging...that potentially is a flag. Be worried about that one." — Dr. Chapa, 21:10

6. Documentation and Clinical Takeaway

(Timestamp: 19:55–22:40)

• Document:
  • Baseline change and its context (variability, decelerations, maternal findings).
  • Recognize as likely physiological if within 110–160 and no other concerning changes.
  • Take action if threshold for tachycardia or bradycardia is crossed, or if zigzag patterns/minimal variability arise.

Notable Quotes and Memorable Moments

• On fluctuating baselines:

  "As long as the baby's heart rate stays between 110 to 160, it is totally normal. ... A change in baseline alone, it has to cross that 160 threshold."
  — Dr. Chapa, 12:30

• On wandering baseline concern:

  "Wandering baselines have a decreased variability, either minimal or absent. That's worrisome."
  — Dr. Chapa, 20:10

• On the normalcy of labor physiology:

  "The baby's heart rate can change baseline, typically because of catecholamine stress intrapartum, which is a normal physical physiologic response to being squished as your home is trying to evict you."
  — Dr. Chapa, 15:20

Timestamps for Important Segments

• 00:31–02:50 — Overview of the three-tier FHT system
• 01:20–03:50 — Listener question breakdown
• 05:15–09:30 — Normal ranges, tachycardia, and when baseline shifts should be considered
• 10:45–13:45 — Clinical discussion on normalcy of FHT baseline change
• 14:45–16:10 — Evidence review: incidence of baseline change
• 18:00–21:30 — Definition, significance, and management of zigzag/wandering baseline
• 19:55–22:40 — Final synthesis: key takeaways and documentation guidance

Summary Table: FHT Baseline Changes in Labor

| Scenario | Variability | Range | Significance | Action | |----------|-------------|-------|--------------|--------| | Baseline shifts but stable | Moderate | 110–160 | Physiologic, common | Document and monitor | | Crosses >160 (tachycardia) | Any | >160 | Evaluate for infection, meds, etc. | Full assessment | | Crossing <110 (bradycardia) | Any | <110 | Pathological if sustained | Assess for cause/intervene | | Zigzag/wandering baseline | Minimal/Absent | Variable | Concerning for hypoxia | Escalate care |

Clinical Pearls (in Dr. Chapa's Words)

• “If the baseline changes within normal brackets, and everything else is alright, that is completely okay.” (12:30)
• “It could be close to 50% of term labors [that] will do that.” (14:40)
• “If it keeps wandering, zigzagging, that potentially is a flag. Be worried about that one.” (21:10)

Bottom Line

A sustained FHT baseline shift within 110–160 bpm, with normal variability and without other clinical/red flag signs, is physiologic and should not prompt alarm. However, zigzag/wandering baselines—especially with diminished variability—are concerning and need further evaluation.

• Baseline change alone ≠ pathology
• Crossing tachycardia/bradycardia thresholds or zigzag patterns = act/investigate

"As long as variability is okay and there's nothing else going on, it's okay to disregard. But it still requires documentation..." — Dr. Chapa, 22:15