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Fetal heart rate monitoring (CTG)
Always read a CTG in the same order — baseline, variability, accelerations, decelerations — and assign category I, II or III; moderate variability is the most reassuring sign, and recurrent late decelerations or absent variability are the danger signs.
Why it matters in the exam
Almost every obstetrics exam has a question that describes a tracing in words and asks for the mechanism or the action. You need to recognise the three types of deceleration: early (head compression, a mirror image of the contraction, benign), variable (cord compression, abrupt fall and rise) and late (uteroplacental insufficiency, a gradual fall whose nadir comes after the peak of the contraction). The decision in the question is usually between continued observation, intrauterine resuscitation and immediate delivery.
Candidates are also asked about causes of baseline change: fetal tachycardia above 160 points to maternal fever or intra-amniotic infection, and prolonged bradycardia may come from placental abruption, uterine rupture or cord prolapse. Minimal variability can come from a fetal sleep cycle or from drugs (opioids, magnesium), and a sinusoidal pattern indicates severe fetal anaemia. Outside labour, a non-stress test is reactive when there are 2 accelerations in 20 minutes.
Key points
- Reading order: baseline, variability, accelerations, decelerations.
- Normal baseline 110–160; moderate variability 6–25.
- Early = head; variable = cord; late = placenta.
- Category III → intrauterine resuscitation and immediate delivery.
- Fetal tachycardia with fever → intra-amniotic infection.
Summary table
| Component | Normal | Abnormal | Meaning |
|---|---|---|---|
| Baseline | 110–160 beats per minute | Above 160 or below 110 for at least 10 minutes | Tachycardia: fever, infection, drugs; bradycardia: abruption, uterine rupture, cord |
| Variability | Moderate, 6–25 beats | Absent or minimal (5 or less); sinusoidal | Moderate variability = no acidaemia at present |
| Accelerations | A rise of 15 beats for 15 seconds after 32 weeks | Absent accelerations alone are not pathological | Reactive NST: 2 accelerations in 20 minutes |
| Early deceleration | Gradual, mirrors the contraction | — | Head compression; benign |
| Variable deceleration | Abrupt fall, less than 30 seconds to the nadir | Recurrent and deep | Cord compression; change position, sometimes amnioinfusion |
| Late deceleration | Gradual fall, nadir after the peak of the contraction | Recurrent (with more than 50% of contractions) | Uteroplacental insufficiency; intrauterine resuscitation |
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Sources
- ACOG Practice Bulletin No. 106, 2009, reaffirmed — Intrapartum Fetal Heart Rate Monitoring: Nomenclature, Interpretation, and General Management Principles
- ACOG Practice Bulletin No. 116, 2010, reaffirmed — Management of Intrapartum Fetal Heart Rate Tracings
- FIGO consensus guidelines on intrapartum fetal monitoring, 2015 — Cardiotocography
- Williams Obstetrics, 26th edition (2022) — Intrapartum Assessment
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.