Intrapartum fetal risk assessment · Version 1.0 · Evans et al., AJOG 2023
How it works: The FRI scores 8 categories — 4 EFM parameters, uterine activity, and three risk factor domains. Each category scores 1 if normal, 0 if abnormal. Total ÷ 8 × 100 = FRI%. Reassess every 10-minute tracing segment; dynamic variables (EFM, uterine activity) may change; risk factor scores generally remain until delivery.
Red zone ≠ deliver now — it initiates expeditious assessment, intrauterine resuscitation, and a 40-minute shot clock. Sentinel events (prolapsed cord, unremitting bradycardia) require immediate delivery regardless of FRI score.
● Green >50%● Yellow 26–50%● Red ≤25% — Abnormal
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● Red ≤25%● Yellow 26–50%● Green >50%
EFM ParametersDynamic · reassess each 10 min
Fetal Heart Rate BaselineNormal: 110–160 bpm · no persistent tachycardia or bradycardia
DecelerationsNormal: absent or early only · Abnormal: recurrent variable or late decelerations
Tap to score
Uterine Activity (FRI threshold)Normal: ≤4 contractions/10 min avg over 30 min · FRI uses >4, not ACOG's >5 — captures false negatives at the 4–5 range
Tap to score
Maternal Risk FactorsScore 0 if ≥1 present
Maternal Risk Factor(s) PresentCardiac disease · hypertension (chronic or PIH/preeclampsia) · SLE · asthma/pulmonary disorder · anemia/hemoglobinopathy · diabetes · thyroid disorder · infection · obesity BMI >35 · AMA · drug abuse/smoking · short stature <5'2" · malabsorption/poor weight gain
Tap to score
Obstetrical Risk FactorsStatic + can develop in labor
All publications underlying the Fetal Reserve Index Calculator
Conflict of interest: Patents on the Fetal Reserve Index are held by M.I. Evans. Co-authors Britt, S. Evans, and Devoe report no conflict of interest. No funding was received for the primary AJOG 2023 publication.
Publications Used in This Tool
1
Evans MI, Britt DW, Evans SM, Devoe LD. Improving the interpretation of electronic fetal monitoring: the fetal reserve index. Am J Obstet Gynecol. 2023;228(5 Suppl):S1129–S1143. doi:10.1016/j.ajog.2022.11.1275
Primary Source · Expert ReviewAJOG 2023
Defines the 8-component FRI scoring system, zone thresholds (green >50%, yellow 26–50%, red ≤25%), and the 40-minute shot clock protocol. Presents head-to-head comparison of FRI vs. ACOG Category system: in the study dataset, FRI sensitivity for CP cases = 100% vs. 45% for Category III and 28% for ACOG monograph criteria. Summarizes 14 refereed published FRI studies encompassing >2,000 control patients.
2
Eden RD, Evans MI, Evans SM, Schifrin BS. The "fetal reserve index": re-engineering the interpretation and responses to fetal heart rate patterns. Fetal Diagn Ther. 2018;43:90–104.
Foundational Validation Study
Original FRI validation. Studied 60 singleton term CP cases vs. 200 controls — all with Category I tracings at labor onset. Only 27% of CP cases had cord pH <7.00 (the ACOG monograph threshold). 100% of CP cases reached the red zone; controls who entered red averaged only ~1 hour there vs. >5 hours for CP cases. Source for component definitions, zone thresholds, and the 40-minute shot clock concept.
3
Eden RD, Evans MI, Evans SM, Schifrin BS. Reengineering electronic fetal monitoring interpretation: using the fetal reserve index to anticipate the need for emergent operative delivery. Reprod Sci. 2018;25:487–497.
Prospective Study · Emergency Deliveries
Prospective study: FRI-guided management reduced emergency operative deliveries from 17% to 4%, attributed to earlier recognition of developing compromise and initiation of resuscitative measures (stopping oxytocin, repositioning, O₂). Primary source for the complete maternal, obstetrical, and fetal risk factor list used in this tool (Table 4 in AJOG 2023).
4
Evans MI, Britt DW, Eden RD, Evans SM, Schifrin BS. The fetal reserve index significantly outperforms ACOG Category system in predicting cord blood base excess and pH. Reprod Sci. 2019;26:858–863.
Head-to-Head · Acid-Base Correlation
Demonstrates FRI provides superior correlation with cord blood pH and base excess compared to the ACOG Category system. Supports use of FRI as a non-invasive surrogate for fetal scalp sampling data and provides physiological basis for earlier intervention.
5
Evans MI, Britt DW, Worth J, Mussalli G, Evans SM, Devoe LD. Uterine contraction frequency in the last hour of labor: how many contractions are too many? J Matern Fetal Neonatal Med. 2021 [Epub ahead of print].
Uterine Activity Threshold
Empirical basis for the FRI-specific uterine activity threshold of >4 contractions/10 min (vs. ACOG's >5). Using 4 as the cutpoint improves sensitivity for detection of decreased cord blood pH and base excess — cases with UCF between 4 and 5 are false negatives at the ACOG threshold but true positives under the FRI threshold.
6
Eden RD, Evans MI, Britt DW, Evans SM, Gallagher P, Schifrin BS. Combined prenatal and postnatal prediction of early neonatal compromise risk. J Matern Fetal Neonatal Med. 2021;34:2996–3007.
Neonatal Period · Postpartum Extension
Shows that fetal reserve depletion (falling pH and base excess) continues for several minutes postdelivery before correcting. Approximately 85% of neonates develop significant tachycardia postnatally. In the highest-risk FRI group (~5% of patients), average neonatal HR reached 185 bpm with persistent variability loss; by 20 minutes, only 28% had returned to ≤160 bpm. Supports monitoring at-risk neonates for at least 30 minutes postdelivery.