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Fetal Monitoring

There are a wide range of clinical techniques and investigations available to healthcare professionals to survey the condition of a fetus in the womb. These may be deployed from early pregnancy to birth. They range from the use of traditional equipment such as a Pinard stethoscope that allows direct auscultation of the fetal heart beat, to ultrasound imaging of the fetus that gives an ever-increasing amount of morphological and functional data about the unborn child.

This article deals with those monitoring techniques that are used immediately preceding or during childbirth – known as intrapartum fetal monitoring. Current techniques rely predominantly on the use of electronic fetal monitoring through the use of cardiotocography (CTG). This technique allows detection and analysis of the fetal heart rate (via Doppler US or direct fetal ECG measurement with a fetal scalp electrode) and a semi-quantitative analysis of myometrial activity and contractions. The interpretation of the data collected depends on the relationship between the two traces.

The technique became widely used from the 1960s onwards. Prior to this there was very little that could be discerned about the state of the fetus. The new technology was widely embraced as an undoubted 'good thing' that would lead to better outcomes and reduce the incidence of conditions such as cerebral palsy that were postulated to be largely due to episodes of intrapartum cerebral ischaemia. Unfortunately, subsequent evidence has not borne out this optimism.

It seems unlikely that more than a small minority of cases of cerebral palsy are directly attributable to avoidable intrapartum fetal hypoxia.1 Also, there appears to be at best a tenuous connection between cardiotocographic findings, what they signify about the fetal condition and any improvement in outcomes as a result of intervention based upon them.2 A Cochrane systematic review has found no evidence of the usefulness of cardiotocography in antepartum fetal assessment, and even a trend to an increase in perinatal deaths in patients being managed using cardioiotocography (odds ratio 2.85, 95% confidence interval 0.99 to 7.12).3 For these reasons, the widespread use of electronic fetal monitoring as part of the management of normal labour is being called into question by professional and lay voices alike.4 A recent Cochrane meta-analysis showed that the use of routine CTG had a minor beneficial effect on the incidence of neonatal seizures, but increased instrumental and caesarean deliveries significantly, calling into question its continuing routine use, against current guideline advice.5

Criticisms of the routine use of electronic fetal monitoring:6
  • Poor understanding of the patho-physiological background of the measurements collected
  • Indirect fetal monitoring treated by some as a direct monitor of fetal condition
  • Numerous technical problems that affect its usefulness
  • Variability in measurement and recording techniques
  • Qualitative nature of information obtained, requiring complex pattern recognition
  • An absence of agreed systems of classification
  • Confusion about the many influences on the fetal heart rhythm and rate
  • Significant intra- and inter-observer variation in interpretation of data
  • Low validity of findings and high false-positive finding rate
  • A screening investigation to detect the presence of fetal distress being misused as a diagnostic tool
  • Inevitably leads to an increase in instrumental or surgical deliveries, due to the high false-positive rate
  • No satisfactory criteria on how, when and who to monitor
  • Contributes significantly to medico-legal vulnerability of doctors who manage childbirth
So what is cardiotocography useful for?

It can be used as a fairly reliable screening test to indicate a normal condition of the fetus. If the fetal heart rate and pattern is normal it is virtually certain that the fetus is not suffering hypoxia, acidaemia or other causes of distress. It is this useful aspect of cardiotocography that led to its widespread adoption. Unfortunately, its ubiquitous presence on labour wards has led to its overzealous use and overcomplicated interpretation, without a solid evidence-based grounding. The table below lists features of the CTG that would lead one to consider it reassuring, non-reassuring or abnormal.

CTG fetal heart rate features and classification7
  Baseline HR/bpm HR Variablity/bpm Decelerations in fetal HR Accelerations in fetal heart rate
Reassuring 110–160 ≥5 Absent Present
Non-reassuring 100–109 or 161–180 <5 for ≥40 mins but <90 mins Early decelerations or variable decelerations or single prolonged deceleration lasting ≤3 mins Absence of accelerations in an otherwise normal CTG is of uncertain significance
Abnormal <100 or >180 or sinusoidal pattern for ≥10 mins <5 for ≥90 mins Atypical variable decelerations or late decelerations or single prolonged deceleration lasting >3 mins Absence of accelerations in an otherwise normal CTG is of uncertain significance

  • A normal CTG is defined as all four features fall into reassuring category.
  • A suspicious CTG is defined as 1 feature non-reassuring, rest reassuring.
  • A pathological CTG is defined as ≥2 features non-reassuring, or ≥1 abnormal.

Who should have electronic fetal monitoring?

The following table of antenatal and intrapartum risk factors should prompt the use of continuous electronic fetal monitoring, according to algorithmic guidelines issued by NICE & RCOG. The lists are not exhaustive and other risk factors may prompt the use of continuous monitoring. All other patients having normal labour without associated risk factors should not have continuous electronic fetal monitoring. They should be monitored with normal partogram assessments and have FHR checked by auscultation for a full minute after uterine contractions and at least every 15 minutes in the first stage of labour, and every 5 minutes in the second stage of labour. All decisions to use continuous electronic fetal monitoring should be discussed with the patient and the reasons for offering it should be outlined. It is important to note that these criteria are only for the offering of continuous electronic fetal monitoring, not its mandatory use, and the pregnant mother is entitled to have the last word on whether or not she wishes to use it. Where it has been recommended and declined, this fact should be carefully documented in the partogram and clinical record.

Indications for continuous electronic fetal monitoring during pregnancy
Antenatal maternal risk factors Antenatal fetal risk factors Intrapartum risk factors
Previous caesarean section Fetal growth restriction Augmentation of labour using oxytocin
Pre-eclampsia Prematurity Epidural analgesia
Post-term pregnancy (>42 weeks) Oligohydramnios Vaginal bleeding during labour
Prolonged membrane rupture (>24 hours) Abnormal placental blood flow as indicated by Doppler artery velocitometry Maternal pyrexia
Induced labour Multiple pregnancies Fresh meconium-stained liquor
Diabetes Meconium-stained liquor  
Ante-partum haemorrhage Breech presentation  
Other significant maternal medical disease    
What action is necessary if a CTG is suspicious or pathological?

For a suspicious CTG:7

  • If the CTG trace is of inadequate quality:
    • Check contact and connections of external transducer.
    • Check contact and connections of fetal scalp electrode (FSE) if being used.
    • Check maternal pulse and ensure not recording this in error.
    • Consider use of FSE if not currently being used.
  • If there is evidence of uterine hypercontractility:
    • Consider discontinuation of oxytocin if being used.
    • Check whether vaginal prostaglandins have been utilised.
    • Consider use of terbutaline or other tocolytic agents.
  • If there is maternal tachycardia/pyrexia:
    • Consider screening investigations and empirical treatment for infection.
    • Consider treatment for maternal dehydration.
    • Consider the effect of tocolytics and discontinuing them if this may be causing the tachycardia.
    • Check maternal BP and consider 500ml infusion of crystalloid if indicated.
  • If there are other relevant maternal adverse factors:
    • Check maternal position and if supine then move into left lateral position.
    • Consider effect of recent vaginal examination.
    • Consider effect of recent bed pan use.
    • Consider effect of recent vomiting or vasovagal episode.
    • Consider effect of recent siting or topping-up of epidural analgesia infusion.
    • Check BP and if low give 500ml infusion of crystalloid if no contraindications to this.

Where a trace continues to be suspicious despite these interventions then observe for other suspicious FHR features, consider whole clinical context and take appropriately experienced obstetric advice on how to proceed.
For a pathological CTG:7

  • If fetal blood sampling is indicated/feasible:
    • Encourage mother to use left lateral position and check BP, giving 500ml crystalloid if appropriate.
    • Proceed to fetal blood sampling with maternal consent.
    • Decide further course on basis of fetal blood sampling results (see table below).
  • If fetal blood sampling is not indicated or not feasible:
    • Use left lateral psoition and BP check with crystalloid infusion as above.
    • Expedite delivery according to anaesthetic, paediatric and experienced obstetric opinion.
    • Speed of delivery should take into account the severity of FHR abnormalities and relevant maternal factors.
    • Current accepted standard is that expedited delivery should occur within 30 minutes. The evidence base for this recommendation, and its real-world practicality, have been questioned. Most practitioners advocate that quick, safe delivery is more important than rapid delivery.8,9

Following delivery, paired umbilical cord samples should be taken and 1- and 5-minute Apgar scores calculated and all results recorded in the mother's and newborn's notes.

A Cochrane systematic review has indicated that when continuous electronic fetal monitoring is indicated, the use of a fetal scalp electrode to measure fetal heart rate and allow ST waveform analysis by ECG, along with CTG, results in fewer blood samples taken from the baby's scalp, less surgical assistance and better oxygen levels at birth than CTG alone.10

Interpretation of fetal blood pH sampling

The table below gives the current RCOG & NICE guidance on appropriate responses to fetal scalp pH results.7

Fetal scalp pH results and apropriate courses of action
Fetal blood sample (FBS) result/pH Subsequent action
≥7.25 Repeat FBS if fetal HR abnormalities persisit
7.21–7.24 Repeat FBS within 30 minutes or consider delivery if rapid fall in pH since last sample
≤7.20 Delivery indicated
All fetal scalp blood pH estimations should be interpreted taking into account the previous pH measurement, the rate of progress in labour and the clinical features of the mother and baby.
Potential future developments in this field

Vibroacoustic stimulation of the fetus as an adjunct to CTG may improve its utility by reducing the incidence of non-reactivity (if, for example, the fetus is sleeping).11 However, a recent Cochrane systematic review found that there is insufficient evidence from randomised trials on which to base recommendations for use of vibroacoustic stimulation in the evaluation of fetal well-being in labour in the presence of a non-reassuring cardiotocographic trace.12 A new method of fetal pulse oximetry may be useful for reducing caesarean section rates in the presence of non-reassuring CTG findings.13 The use of automated computerised analysis systems to interpret CTGs and avoid intra- and inter-observer variability is being shown to have some beneficial effects in trials and offers hope of more consistent criteria for intervention on the basis of CTG findings in future.14 The combination of auto-analysis of fetal pulse oximetry and CTG data is also being investigated with some evidence of usefulness.15

Conclusion

Continuous electronic fetal monitoring is a useful intrapartum tool in experienced hands, if used selectively and according to evidence-based guidelines. It should not be used routinely as this is one of the factors that has pushed up the instrumental and caesarean delivery rates in the developed world. Its use should continue to be investigated by carefully designed randomised controlled trials to optimise its utility and help improve and develop guidelines for its use.

Document References
  1. Keogh JM, Badawi N; The origins of cerebral palsy.; Curr Opin Neurol. 2006 Apr;19(2):129-34. [abstract]
  2. Parer JT, King T, Flanders S, et al; Fetal acidemia and electronic fetal heart rate patterns: Is there evidence of an association?; J Matern Fetal Neonatal Med. 2006 May;19(5):289-94. [abstract]
  3. Pattison N, McCowan L; Cardiotocography for antepartum fetal assessment.; Cochrane Database Syst Rev. 2000;(2):CD001068. [abstract]
  4. Kitzinger S, Green JM, Chalmers B, et al; Why do women go along with this stuff?; Birth. 2006 Jun;33(2):154-8. [abstract]
  5. Thacker SB, Stroup D, Chang M; Continuous electronic heart rate monitoring for fetal assessment during labor.; Cochrane Database Syst Rev. 2001;(2):CD000063. [abstract]
  6. van Geijn H; Cardiotocography, ObGyn.net, 1998 [Full Text]; An objective overview of the use of cardiotocography from a practising obstetrician
  7. Electronic fetal monitoring algorithm derived from NICE/RCOG guidelines; Useful algorithmic summary of the 2001 NICE/RCOG guideline.
  8. Thomas J, Paranjothy S, James D; National cross sectional survey to determine whether the decision to delivery interval is critical in emergency caesarean section.; BMJ. 2004 Mar 20;328(7441):665. Epub 2004 Mar 15. [abstract]
  9. MacKenzie IZ, Cooke I; What is a reasonable time from decision-to-delivery by caesarean section? Evidence from 415 deliveries.; BJOG. 2002 May;109(5):498-504. [abstract]
  10. Neilson JP; Fetal electrocardiogram (ECG) for fetal monitoring during labour.; Cochrane Database Syst Rev. 2003;(2):CD000116. [abstract]
  11. Tan KH, Smyth R; Fetal vibroacoustic stimulation for facilitation of tests of fetal wellbeing.; Cochrane Database Syst Rev. 2001;(1):CD002963. [abstract]
  12. East CE, Smyth R, Leader LR, et al; Vibroacoustic stimulation for fetal assessment in labour in the presence of a nonreassuring fetal heart rate trace.; Cochrane Database Syst Rev. 2005 Apr 18;(2):CD004664. [abstract]
  13. East CE, Chan FY, Colditz PB; Fetal pulse oximetry for fetal assessment in labour.; Cochrane Database Syst Rev. 2004 Oct 18;(4):CD004075. [abstract]
  14. Ojala K, Vaarasmaki M, Makikallio K, et al; A comparison of intrapartum automated fetal electrocardiography and conventional cardiotocography--a randomised controlled study.; BJOG. 2006 Apr;113(4):419-23. [abstract]
  15. Salamalekis E, Siristatidis C, Vasios G, et al; Fetal pulse oximetry and wavelet analysis of the fetal heart rate in the evaluation of abnormal cardiotocography tracings.; J Obstet Gynaecol Res. 2006 Apr;32(2):135-9. [abstract]
Internet and Further Reading Acknowledgements EMIS is grateful to Dr Sean Kavanagh for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 1063
Document Version: 20
DocRef: bgp220
Last Updated: 29 Aug 2006
Review Date: 28 Aug 2008






















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