ACOG Menu

Careers |

Countdown to Intern Year, Week 4: Fetal Heart Tracings

We can’t believe we’ve already reached the 4th and final week of our Countdown to Intern Year series! You can check out all our previous content here if you didn’t get a chance to see it. We’ll be concluding our series with a review of Fetal Heart Tracings. Remember to check out the additional resources below, including advice from our seasoned JFAC young physicians and links to ACOG wellness and clinical resources. We’ve also included information on the #OBGYNInternChallenge via @Creogsovercoffee

Your JFAC wishes you the best of luck as you start this rewarding journey.  Don’t hesitate to reach out to us for anything as you progress through your career. Best of luck!


Week 4: Fetal Heart Tracings

Classification and Interpretation

Content adapted from relevant ACOG Practice Bulletins and AAFP Guidelines

While EFM use may be common and widespread, there is controversy about its efficacy, interobserver and intraobserver variability, and management algorithms. While it can be an important tool to assess fetal wellbeing, it is also limited by its high false-positive rate. That being said, it’s still critical for you to know how to interpret a strip. 

A Systematic Approach to FHR Interpretation 

The interpretation of the fetal heart rate tracing should follow a systematic approach with a full qualitative and quantitative description. Check out a suggested systematic approach from the AAFP below!
 
The interpretation of the fetal heart rate tracing should follow a systematic approach with a comprehensive description of the following:

  1. Baseline rate
  2. Baseline fetal heart rate (FHR) variability
  3. Presence of accelerations
  4. Periodic or episodic decelerations
  5. Changes or trends of FHR patterns over time
  6. Frequency and intensity of uterine contractions

Before I get to the Fetal Heart Tracing (FHT), how do I describe my patient’s uterine contractions?

*Remember, top strip - FHT; bottom strip - uterine contractions.

  • Normal: five contractions or less in 10 minutes, averaged over a 30-minute window
  • Tachysystole: more than five contractions in 10 minutes, averaged over a 30-minute window
    • Always include presence or absence of associated FHR decelerations
    • Applies to both spontaneous and stimulated labor
 

Understanding and Describing Elements of the FHT

1. Identifying the baseline FHT rate and the presence of variability

Pattern

Description

Baseline
*bpm = beats per minute

 

Must be for a minimum of 2 minutes in any 10-minute segment. 

  • Normal FHR baseline: 110–160 bpm
  • Tachycardia: FHR baseline > than 160 bpm
  • Bradycardia: FHR baseline < than 110 bpm
 

Baseline Variability

Fluctuations in the baseline FHR that are irregular in amplitude and frequency. Calculated as amplitude of peak-to-trough in bpm. 

  • Absent: amplitude undetectable 
  • Minimal: amplitude <  5 bpm 
  • Moderate (normal): amplitude 6–25 bpm
  • Marked: amplitude > 25 bpm
 

 
2. Identifying accelerations

Pattern

Description

Acceleration
*bpm = beats per minute

Visually apparent, abrupt (onset to peak < 30 seconds) increase in FHR from baseline.

  • < 32 weeks EGA: peak ≥ 10 bpm above baseline, duration ≥ 10 seconds but < 2 minutes from onset of the acceleration to return to baseline.
  • ≥ 32 weeks EGA: peak ≥ 15 bpm above baseline, duration ≥ 15 seconds but < 2 minutes from onset of the acceleration to return to baseline.

 

 
3. Identify decelerations

Type of Deceleration

Definition

Early deceleration

  • Symmetrical gradual decrease and return of the FHR associated with a uterine contraction
  • Nadir of the deceleration = peak of the contraction. 
 

Late deceleration

  • Onset, nadir, and recovery of the deceleration occur after the beginning, peak, and ending of the contraction, respectively.

Variable deceleration

  • Decrease in FHR is 15 bpm or greater, lasting  ≥ 15 seconds, and < 2 minutes in duration. 
  • Onset, depth, and duration commonly vary with successive uterine contractions.
 

Prolonged deceleration

  • Decrease in FHR from the baseline that is 15 bpm or more, lasting 2 minutes or more but less than 10 minutes in duration

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.
  • Not good. 
 

For examples, please see the Perinatology website's Intrapartum Fetal Heart Rate Monitoring page.

Assigning FHR Patterns to Categories

ACOG recommends using a three-tiered system for the categorization of FHR patterns. 

Category I

Category I FHR tracings include all of the following:

  • Baseline rate: 110-160 beats per minute
  • Baseline FHR variability: moderate
  • Late or variable decelrations: absent
  • Early decelerations: present or absent
  • Accelerations: present or absent

Category II

Category II FHR tracings include all FHR tracings not categorized as Category I or Category III. Category II tracings may represent an appreciable fraction of those encountered in clinical care. Examples of Category II FHR tracings include any of the following:

Baseline rate

  • Bradycardia not accompanied by absent baseline variability
  • Tachycardia

Baseline FHR variability

  • Minimal baseline variability
  • Absent baseline variability with no recurrent decelerations
  • Marked baseline variability

Accelerations

  • Absence of induced accelerations after fetal stimulation

Periodic or episodic decelerations

  • Recurrent variable decelarations accompanied by minimal or moderate baseline variability
  • Prolonged deceleration more than 2 minutes but less than 10 minutes
  • Recurrent late declarations with moderate baseline variability
  • Variable decelerations with other characteristics such as slow return to baseline, overshoots, or "shoulders" 

Category III

Category III FHR tracings include either

  • Absent baseline FHR variability and any of the following:
    • Recurrent late decelarations
    • Recurrent variable decelerations
    • Bradycardia
  • Sinusoidal pattern

Interpretation and Management

*general algorithm 

Category Interpretation

Category I

Strongly predictive of normal fetal acid–base status

Category II

Not predictive of abnormal fetal acid–base status, yet presently there is not adequate evidence to classify these as Category I or Category III.

Category III

Abnormal fetal acid–base status cannot be ruled out

It is important to recognize that FHR tracing patterns provide information only on the current acid–base status of the fetus. Tracing patterns can and will change!

 

 Figure 1. Management algorithm of intrapartum fetal heart rate tracings based on three-tiered category system. Abbreviation: FHR, fetal heart rate.

 

For more information on the use, interpretation and management of patients based on Fetal Heart Tracings check out the resources below. If you have any feedback on our “Countdown to Intern Year” series, please reach out to Samhita Nelamangala at d4medstudrep@gmail.com

Relevant ACOG Resources

Video Resources

General Resources