A contextualized way to read electronic fetal monitoring — turning a subjective tracing into a quantitative 8-point score that flags a fetus at risk earlier than the ACOG Category system. Build a score, explore the risk factors, and see how it performs.
Electronic fetal monitoring (EFM) is used in nearly 90% of US labors, yet much of the confusion around it comes from treating a screening test as if it were a diagnostic one. EFM does not diagnose fetal injury — it screens for risk. The Fetal Reserve Index (FRI) is built on that distinction.
Each of the 8 categories scores 1 if normal, 0 if not. The total, divided by 8 and multiplied by 100, is the FRI. Toggle the tracing features and uterine activity directly; for the three risk-factor categories, tick any item to flag that category. Watch the score and zone update live.
| Points (of 8) | FRI % | Zone |
|---|---|---|
| 8 / 8 | 100 | Green |
| 7 / 8 | 87.5 | Green |
| 6 / 8 | 75.0 | Green |
| 5 / 8 | 62.5 | Green |
| 4 / 8 | 50.0 | Yellow |
| 3 / 8 | 37.5 | Yellow |
| 2 / 8 | 25.0 | Red |
| 1 / 8 | 12.5 | Red |
| 0 / 8 | 0 | Red |
Zones: Green >50% · Yellow 50%–26% · Red ≤25%. Source: Evans et al. AJOG 2023;228(5S):S1129–S1143.
Four come straight off the tracing. One captures how hard the uterus is working. Three capture the clinical context. In version 1.0 of the FRI, all eight are weighted equally — each worth one point.
| # | Category | What it captures |
|---|---|---|
| 1 | Fetal heart rate | Baseline rate within normal range |
| 2 | Baseline variability | Moderate variability present |
| 3 | Accelerations | Presence of accelerations |
| 4 | Decelerations | Absence of significant decelerations |
| 5 | Increased uterine activity | Contraction frequency at or below threshold |
| 6 | Maternal risk factors | None present (see Risk Factors tab) |
| 7 | Obstetrical risk factors | None present |
| 8 | Fetal risk factors | None present |
Each factor scored 1 if normal, 0 if not. Maximum 8/8 = 100%. Source: Evans et al. AJOG 2023.
The risk factors (categories 6–8) are generally static — once a category loses its point, it usually stays lost until delivery. The four tracing features and uterine activity (categories 1–5) are dynamic — they change as labor progresses, with pushing and descent, and in response to intrauterine resuscitation. The FRI is recalculated for each 10-minute segment of monitoring.
These are the maternal, obstetrical, and fetal conditions that cost a category its point. The presence of any item flags that whole category. They are organized by how they threaten the fetus — perfusion, oxygen delivery, and the safety of vaginal delivery.
Adapted from Eden et al. as presented in Evans et al. AJOG 2023, Table 4. Standard ACOG definitions are used for all tracing components.
In the authors' original series — 60 singleton term babies who entered labor with reassuring Category I tracings and went on to develop cerebral palsy, compared with 200 controls — the same cases were scored three ways. The sensitivity for identifying those CP cases differed sharply.
In-sample sensitivity, original 60-case CP series vs 200 controls. The authors note FRI sensitivity will never be 100% in real-world practice. Source: Evans et al. AJOG 2023.
The retrospective standard the FRI is designed to anticipate. It tells you what likely happened — but only after the fact, and with rigid cutoffs (pH <7.00) that miss many CP cases.
Source: ACOG. Neonatal Encephalopathy and Neurologic Outcome, 2014 (Table 1 in Evans et al. 2023). HIE = hypoxic-ischemic encephalopathy.
The FRI is not the first attempt to improve on visual tracing reading. Many automated and AI systems came before it — most rule-based, some using neural networks. A recurring theme: large trials repeatedly failed to show better perinatal outcomes.
| System | Authors | Design | Data analyzed | Year |
|---|---|---|---|---|
| Oxford Sonicaid | Dawes et al | Rule-based | Antepartum FHR | 1996 |
| NST-Expert | Alonso-Betanzos et al | Rule-based | Antepartum FHR | 1992 |
| INFANT | INFANT Collaborative | Rule-based + AI | Intrapartum FHR | 2007 |
| SIS-Porto | Ayres-de-Campos et al | Rule-based | Intrapartum FHR | 2000 |
| PeriCALM | Elliott et al | Rule-based + AI | Intrapartum FHR | 2010 |
| STAN | Olofsson et al | Rule-based | Intrapartum FHR + fetal ECG | 2014 |
| (neural network) | Georgieva et al | AI | Intrapartum FHR | 2013 |
Source: Evans et al. AJOG 2023, Table 2. FHR = fetal heart rate.
For centuries, diagnosing a heart attack was a gestalt of signs and symptoms. The ECG helped; then CPK isoenzymes and troponin turned it into a number anyone could read, with the same conclusion every time. The authors' goal is the same for EFM — a quantitative metric so that reading fetal status becomes as reproducible as reading a lab result.
Reaching the red zone is not an order to deliver. It starts a clock — borrowed from basketball — that forces a structured, time-bound response before the situation deteriorates.
This is a call for expeditious assessment by senior staff who can evaluate the whole picture. Intrauterine resuscitation is usually the first step:
Version 1 of the protocol allows up to 40 minutes to get out of the red zone. The authors are explicit that 40 minutes is an arbitrary but reasonable starting point that may change as more data accrue.
A 30-minute-to-delivery protocol begins, consistent with ACOG guidelines.
Analyzing continuous neonatal heart-rate and acid-base data, the authors found that fetal reserve keeps falling for several minutes after birth before it recovers — and how long recovery takes tracks with the last FRI score before delivery.
Newborns grouped by their last FRI score before delivery. The lower the reserve at birth, the longer recovery took.
Log-rank χ² = 20.02, P < .001. The worst-FRI group (~5% of patients) averaged a neonatal tachycardia of 185 bpm with persistent loss of variability. Source: Evans et al. AJOG 2023, Figure 8.