How to Classify Electronic Fetal Monitor (EFM) Patterns: Categories 1, 2 & 3 Explained
Last week, I walked you through how to interpret an electronic fetal monitor (EFM) tracing—identifying the baseline fetal heart rate, assessing variability, and noting the presence or absence of accelerations and decelerations. If you missed that breakdown, I recommend starting there.
This week, I’m diving deeper. Once you’ve identified those individual tracing components, how do you determine if the strip is normal, abnormal, or somewhere in between? That’s where the three-tiered classification system comes in.
But first, a quick reminder: if you’ve just matched into OB/GYN residency, don’t forget to download my free OB/GYN Residency Starter Pack: A 5-Step Guide for Incoming Interns. I created this guide for my past self—a little something to help you feel prepared for day one without overwhelming you in these final months before residency begins.
The Need for Standardization
Prior to 2008, there was no standardized method for documenting or describing EFM tracings. Some providers referred to them as either “reassuring” or “non-reassuring,” which left a lot of room for interpretation and lacked clinical precision.
In 2008, a large consensus conference was held, bringing together major stakeholders—including ACOG, SMFM, NICHD, and others—to create a standardized system. The result was the three-tiered classification system that we use today.
Why It Matters
As a clinician, you’re expected to describe a tracing (baseline, variability, accelerations, decelerations) and assign it to the correct category: 1, 2, or 3. Here's what each category means.
Category I: Normal
These tracings are strongly predictive of normal fetal acid-base status.
To be Category I, all of the following must be noted:
Baseline heart rate between 110–160 bpm
Moderate variability
Accelerations: May be present or absent
Early decelerations: May be present or absent
No late or variable decelerations
Think of Category I as “reassuring” or low-risk.
Category III: Abnormal
These tracings may be predictive of abnormal fetal acid-base status and require prompt evaluation and possible intervention.
The following findings make a tracing Category III:
Absent variability plus any of the following:
Recurrent late decelerations
Recurrent variable decelerations
Bradycardia
A sinusoidal pattern (regardless of other components)
Recurrent decelerations are defined as those occurring with 50% or more of contractions in a 20-minute window.
Category II: Indeterminate
This includes all tracings that don’t meet the criteria for Category I or III. It’s the “gray zone” of fetal monitoring—often requiring continued surveillance, intervention and then re-evaluation.
Examples of Category II scenarios:
Tachycardia with moderate variability and no decels
Absent variability with intermittent variable decels
Bradycardia with moderate variability and no decels
Let’s Practice
Here are a few examples with their correct classifications:
150 bpm, moderate variability, accels present, no decels → Category I
175 bpm, moderate variability, no accels, no decels → Category II
160 bpm, absent variability, accels present, intermittent variables → Category II
130 bpm, absent variability, no accels recurrent late decels → Category III
130 bpm, moderate variability, no accels, recurrent early decels → Category I
Clinical Significance
Some studies have shown that Category II and III patterns may be associated with neonatal morbidity, including respiratory distress and fetal acidemia. However, other studies show that most Category II and III tracings still result in neonates with normal cord pH values. So while these patterns can offer clinical clues, they aren’t perfect predictors.
In high-risk pregnancies, continuous EFM remains the standard of care due to its potential to reduce neonatal seizures and identify concerning patterns early. For low-risk pregnancies, intermittent auscultation may be appropriate, but that decision depends on the clinical context.
For a deeper dive, I recommend:
Key Takeaway
When presenting or documenting an EFM strip:
Identify the baseline heart rate
Note the variability
Document the presence or absence of accelerations
Document the presence or absence and type of decelerations
Assign the tracing to Category I, II, or III
Want more guidance as you prepare for residency? Grab the free OB/GYN Residency Starter Pack!
See you next Saturday.
K
