Intrapartum CTG interpretation

It is 02:40 and the midwife hands you a trace. The baseline has crept from 135 to 158 over ninety minutes, the decelerations have started coming with every contraction, and the woman has been on oxytocin for six hours. She feels fine. The examiner will not ask you whether you are worried — they will ask you what you saw, in what order, and what you did about it.^[1][6]

That is the whole of intrapartum fetal surveillance. Systematic description, honest classification, then the clinical picture. This topic is built to the RANZCOG Fetal Surveillance Education Program spine, because that is the syllabus the College examines you against.^[17][20]

Overview — what a CTG actually measures

A CTG measures two things and infers a third. It measures the fetal heart rate over time and the frequency of uterine contractions; it infers fetal oxygenation from how the heart responds.^[1][2]

• It never measures oxygen. No CTG has ever recorded a partial pressure. It records a reflex, and reflexes have many causes.^[2][7]
• It is a screening test, not a diagnostic one. Its strength is a very high negative predictive value: a genuinely normal trace almost never accompanies a fetus becoming acidotic in front of you. Its weakness is the false positive.^[1][15]
• It changes one outcome. Compared with intermittent auscultation, continuous CTG halves neonatal seizures — and buys that with more caesareans and more instrumental births.^[4]

^{[1] [4]}

Say that trade-off out loud at the station. Candidates who can quote the seizure benefit and the caesarean cost sound like consultants; candidates who only quote one sound like advocates.^[4][15]

References20ShowHide

1. [1]Ayres-de-Campos D, Spong CY, Chandraharan E FIGO consensus guidelines on intrapartum fetal monitoring: Cardiotocography Int J Gynaecol Obstet, 2015.PMID 26433401
2. [2]Ayres-de-Campos D, Arulkumaran S FIGO consensus guidelines on intrapartum fetal monitoring: Physiology of fetal oxygenation and the main goals of intrapartum fetal monitoring Int J Gynaecol Obstet, 2015.PMID 26433399
3. [3]Visser GH, Ayres-de-Campos D FIGO consensus guidelines on intrapartum fetal monitoring: Adjunctive technologies Int J Gynaecol Obstet, 2015.PMID 26433402
4. [4]Alfirevic Z, Devane D, Gyte GM, et al. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour Cochrane Database Syst Rev, 2017.PMID 28157275
5. [5]Macones GA, Hankins GD, Spong CY, et al. 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.PMID 18757666
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7. [7]Lear CA, Wassink G, Westgate JA, et al. The peripheral chemoreflex: indefatigable guardian of fetal physiological adaptation to labour J Physiol, 2018.PMID 29604081
8. [8]Lear CA, Westgate JA, Bennet L, et al. Fetal defenses against intrapartum head compression-implications for intrapartum decelerations and hypoxic-ischemic injury Am J Obstet Gynecol, 2023.PMID 34801443
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18. [18]Anteby M, Dominsky O, Van Mil L, et al. Interpreting fetal heart rate monitoring in undiagnosed severe fetal anemia-rethinking the sinusoidal pattern Am J Obstet Gynecol, 2025.PMID 40545210
19. [19]Muraoka J, Kodama Y, Ohashi M, et al. Intrapartum fetal heart rate patterns and perinatal outcome in chorioamnionitis at or beyond 34 weeks of gestation J Obstet Gynaecol Res, 2021.PMID 33403794
20. [20]Yeoh M, Ameratunga D, Lee J, et al. Simplifying the language of fetal monitoring Aust N Z J Obstet Gynaecol, 2019.PMID 30460717