Birth · Emergency
CTG Categorization (NICHD)
Intrapartum cardiotocography (CTG) categorization per Macones 2008 NICHD consensus / ACOG PB 229 (2010, reaffirmed 2021). Three tiers: Category I (normal), II (indeterminate), III (abnormal — immediate intervention).
Last reviewed 25 May 2026
NICHD CTG categorisation
Intrapartum fetal heart trace — I / II / III
Baseline (bpm)
Variability
Accelerations
Decelerations
Select all four CTG features to categorise.
Educational tool only — not medical advice. Macones 2008 NIH workshop / ACOG PB 229 (2010, reaffirmed 2021). Category III is uncommon but predictive of abnormal fetal acid-base status. The MAJORITY of intrapartum CTGs are Category II — a heterogeneous group requiring clinical judgement and serial reassessment.
What does this mean?
The NICHD CTG categorisation (Macones 2008 / ACOG PB 229) groups intrapartum fetal heart rate tracings into three buckets. Category I: completely normal — strongly predictive of normal fetal acid-base; routine care. Category III (sinusoidal pattern OR absent variability + late/variable decels or bradycardia): predictive of abnormal acid-base; expedite delivery, intrauterine resuscitation NOW (position change, IV fluid bolus, oxygen, stop oxytocin, treat hyperstimulation). The catch: most intrapartum tracings are Category II — everything that isn’t Cat I or III — a heterogeneous bag requiring clinical judgement, serial reassessment, and a low threshold for fetal scalp blood sampling, fetal scalp stimulation, or proceeding to delivery if not progressing. Cochrane reviews show continuous EFM increases C-section rate without clear long-term benefit in low-risk labour vs intermittent auscultation — so risk-stratify who needs it.
Introduction
The NICHD 2008 (Macones et al.) three-tier intrapartum CTG categorization is the operative standard in the US and widely used internationally. It replaced the older "reassuring / non-reassuring" terminology with explicit feature-based criteria, improving interrater reliability and communication.
The three categories
Category I (Normal)
ALL of:
- Baseline 110-160 bpm.
- Moderate variability (6-25 bpm).
- Accelerations may or may not be present.
- No late or variable decelerations.
- Early decelerations may be present.
Strongly predictive of normal fetal acid-base status.
Category III (Abnormal)
Sinusoidal pattern OR absent variability with any of:
- Recurrent late decelerations.
- Recurrent variable decelerations.
- Bradycardia (< 110 bpm).
Predictive of abnormal fetal acid-base status. Immediate intervention.
Category II (Indeterminate)
Everything else — anything that isn’t Category I or III. About 80 % of intrapartum CTGs are Category II at some point. A heterogeneous group requiring clinical judgement and serial reassessment.
Management by category
Category I
Continue routine surveillance — intermittent (low-risk) or continuous monitoring per protocol.
Category II
Evaluate and correct reversible causes:
- Maternal position change (left lateral).
- IV fluid bolus.
- Treat hypotension (e.g. after epidural).
- Stop oxytocin if uterine hyperstimulation.
- Supplemental oxygen (controversial — Cochrane neutral).
- Treat infection (chorioamnionitis).
- Reassess every 30 minutes.
Category III
Immediate intervention:
- All Category II interventions above.
- Tocolysis (terbutaline) for hyperstimulation.
- Senior obstetric input.
- If pattern persists 10-30 minutes: prepare for expedited delivery — instrumental vaginal if imminent, caesarean otherwise.
Limitations
- Significant interrater variability even with the three-tier system.
- Category II is a wide bucket; no validated sub-categorisation.
- CTG has limited specificity — false-positive rates are high. Continuous CTG in low-risk pregnancies increases caesarean rates without reducing perinatal mortality (Cochrane 2017).
- Educational only; intrapartum decisions are made by the obstetric team in real-time.
Sources
- Macones GA, Hankins GD, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. Obstet Gynecol 2008;112:661-6.
- ACOG. Practice Bulletin 229: Antepartum Fetal Surveillance. 2021.
- ACOG. Practice Bulletin 116: Management of Intrapartum Fetal Heart Rate Tracings. 2010, reaffirmed.
- NICE. Intrapartum care for healthy women and babies (NG194). 2014, updated.
- Alfirevic Z, Devane D, Gyte GML, Cuthbert A. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev 2017;2:CD006066.
Frequently asked questions
What is CTG?
Cardiotocography — continuous electronic monitoring of fetal heart rate and uterine contractions during labour (intrapartum CTG) or in antenatal surveillance (NST). NICHD 2008 (Macones et al., Obstet Gynecol) introduced a 3-tier categorical system for intrapartum CTG interpretation, endorsed by ACOG PB 229 (2010, reaffirmed 2021), to standardise communication and management. The system replaces older variable terminology like 'non-reassuring' and 'reassuring'.
What are the three categories?
Category I (Normal): baseline 110-160 bpm, moderate variability (6-25 bpm), accelerations may or may not be present, no late or recurrent variable decelerations. Strongly predictive of normal fetal acid-base status. Category II (Indeterminate): everything that's not Category I or III — a heterogeneous group requiring clinical judgement. Category III (Abnormal): sinusoidal pattern OR absent variability with recurrent late/variable decelerations or bradycardia. Predictive of abnormal fetal acid-base status; immediate intervention indicated.
Why is Category II so broad?
Because most intrapartum CTGs (~80 %) are Category II, and they range from very mildly abnormal (one variable deceleration with rapid return) to nearly Category III (recurrent variables with minimal variability). The category is intentionally broad because no validated subcategorisation exists. Clinical judgement, serial reassessment, and treatment of reversible causes (position, hydration, hypotension, hyperstimulation) drive management. The Parer-Ikeda 5-tier system and the FIGO 2015 categorisation are alternatives but neither has won out.
What should happen with a Category III?
Immediate intervention: reposition (left lateral), IV fluid bolus, supplemental oxygen, stop oxytocin if running, treat hypotension or hyperstimulation. If pattern persists despite intrauterine resuscitation, expedite delivery — instrumental vaginal if imminent, or caesarean. Senior obstetric input. Category III is uncommon (1-2 % of labours) but strongly predictive of abnormal fetal acid-base status and warrants the response of an obstetric emergency.
What are the four CTG features being assessed?
BASELINE rate (normal 110-160; tachycardia > 160; bradycardia < 110). VARIABILITY (absent / minimal ≤ 5 / moderate 6-25 / marked > 25; sinusoidal pattern is separate). ACCELERATIONS (≥ 15 bpm × 15 sec for ≥ 32 weeks; ≥ 10 bpm × 10 sec for < 32 weeks). DECELERATIONS (early / variable / late / prolonged, classified by frequency as intermittent < 50 % or recurrent ≥ 50 % of contractions). Each feature is interpreted in the context of the full trace and clinical situation.
What about intermittent auscultation vs continuous CTG?
NICE NG194 and Cochrane 2017 (Alfirevic) both find that continuous CTG in low-risk pregnancies increases caesarean rates without reducing perinatal mortality. INTERMITTENT AUSCULTATION (with a hand-held Doppler or Pinard stethoscope every 15 min in active first stage, every 5 min in second stage) is the recommended default for low-risk women. Continuous CTG is indicated for high-risk: induction, augmentation, prior c-section, hypertension, GDM, prematurity, abnormal IA, meconium-stained liquor, abnormal antenatal Doppler.
Can I see my own CTG?
Sometimes. NHS practices vary — some units show the trace to labouring women if they ask; others are more reserved. The trace is part of your medical record and accessible afterwards. Real-time interpretation requires training; even experienced clinicians have inter-rater variability. Don't try to interpret your own trace — focus on the conversation with your team.