Fetal surveillance modalities in labour: intermittent auscultation, fetal scalp electrode, telemetry

Two women are labouring on your ward. One is a well 26-year-old at 39 weeks in spontaneous labour with clear liquor; the other is 41+3 weeks, induced, on oxytocin, with an epidural and a body mass index of 44. Both deserve a considered answer to the same question — how are we going to listen to this baby, and what will we do when we cannot hear it?^[19][3]

Monitoring is a choice with costs. Get it right and you find the compromised fetus early. Get it wrong and you either miss the deterioration or pin a well woman to a bed and operate on a normal baby.^[3][5]

Overview — the modalities and what each one really measures

^{[19] [3]}

• Intermittent auscultation — a Pinard stethoscope or a hand-held Doppler, counting the rate over a defined interval at a defined moment. It samples; it does not record.^[1][2]
• External CTG — an ultrasound transducer plus a tocodynamometer, both strapped to the abdomen. The rate is derived by autocorrelation, so the signal is smoothed and can lock onto the wrong heart.^[20][16]
• Fetal scalp electrode — a spiral electrode in the fetal scalp recording a true fetal electrocardiogram, R-wave to R-wave. Fewer artefacts, better variability, invasive.^[17][6]
• Telemetry and beltless abdominal fetal ECG — the same continuous recording, delivered wirelessly, so the woman can walk, kneel or use water.^[10][12]
• Intrauterine pressure catheter — the only device that measures intrauterine pressure in absolute terms rather than inferring it.^[19][20]

References20ShowHide

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2. [2]Martis R, Emilia O, Nurdiati DS, et al. Intermittent auscultation (IA) of fetal heart rate in labour for fetal well-being Cochrane Database Syst Rev, 2017.PMID 28191626
3. [3]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
4. [4]Smith V, Begley C, Newell J, et al. Admission cardiotocography versus intermittent auscultation of the fetal heart in low-risk pregnancy during evaluation for possible labour admission - a multicentre randomised trial: the ADCAR trial BJOG, 2019.PMID 30126064
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9. [9]Viscarello RR, Copperman AB, DeGennaro NJ Is the risk of perinatal transmission of human immunodeficiency virus increased by the intrapartum use of spiral electrodes or fetal scalp pH sampling? Am J Obstet Gynecol, 1994.PMID 8141193
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18. [18]Blix E, Maude R, Hals E, et al. Intermittent auscultation fetal monitoring during labour: A systematic scoping review to identify methods, effects, and accuracy PLoS One, 2019.PMID 31291375
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