A wide range of clinical techniques and investigations is 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's stethoscope, which allows direct auscultation of the fetal heartbeat, to ultrasound imaging of the fetus, which 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 (FHR) (via Doppler ultrasound 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' which would lead to better outcomes and reduce the incidence of conditions such as cerebral palsy, which 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 is directly attributable to avoidable intrapartum fetal hypoxia:
- Low gestational age (24-30 weeks), postnatal dexamethasone use, patent ductus arteriosus, severe hyaline membrane disease, resuscitation in the delivery room and intraventricular haemorrhage have all been shown to be associated with higher rates of cerebral palsy, whereas antenatal corticosteroid is associated with a lower rate.
- 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.
- 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 cardiotocography.
- The widespread use of electronic fetal monitoring as part of the management of normal labour has been discarded, as a result of professional and public voices.
- A 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.
Criticisms of the routine use of electronic fetal monitoring
- Poor understanding of the pathophysiological 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 whom to monitor.
- Contributes significantly to medicolegal 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 (FHR) and pattern are 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 (CTG) 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. There are four features of a CTG that can be classified:
- Baseline FHR: reassuring 110-160 beats per minute (bpm); non-reassuring 100-109 or 161-180 bpm; Abnormal less than 100 bpm, greater than 180 bpm or a sinusoidal pattern for more than 10 minutes.
- Variability: reassuring has more than 5 bpm; non-reassuring has less than 5 for 40-90 minutes; abnormal has less than 5 for more than 90 minutes.
- Decelerations: reassuring - none present; non-reassuring has typical variable decelerations with over 50% of contractions, occurring for over 90 minutes or a single prolonged deceleration for up to 3 minutes; abnormal has either atypical variable decelerations with over 50% of contractions or late decelerations, both for over 30 minutes or a single prolonged deceleration for more than 3 minutes.
- Accelerations: reassuring has accelerations present. However, the absence of accelerations with otherwise normal trace is of uncertain significance.
A normal CTG has all four features that are reassuring. A suspicious CTG has one feature which is non-reassuring, but the others are reassuring. A pathological CTG has ≥2 features which are non-reassuring, or ≥1 abnormal.
Further information about classifying FHR traces:
- If repeated accelerations are present with reduced variability, the FHR trace should be regarded as reassuring.
- True early uniform decelerations are rare and benign, and therefore they are not significant.
- Most decelerations in labour are variable.
- If a bradycardia occurs in the baby for more than 3 minutes, urgent medical aid should be sought and preparations should be made urgently to expedite the birth of the baby. This could include moving the woman to theatre if the fetal heart has not recovered by 9 minutes. If the fetal heart recovers within 9 minutes the decision to deliver should be reconsidered, in conjunction with the woman if reasonable.
- A tachycardia in the baby of 160-180 bpm, where accelerations are present and no other adverse features appear, should not be regarded as suspicious. However, an increase in the baseline heart rate, even within the normal range, with other non-reassuring or abnormal features should increase concern.
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 the National Institute for Health and Clinical Evidence (NICE) and the Royal College of Obstetricians and Gynaecologists (RCOG). The lists are not exhaustive and other risk factors may prompt the use of continuous monitoring.
|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|
|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|
|Antepartum haemorrhage||Breech presentation|
|Other significant maternal medical disease|
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.
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 fetal heart rate (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.
A Cochrane systematic review has indicated that when continuous electronic fetal monitoring is indicated, the use of a fetal scalp electrode to measure FHR and allow ST waveform analysis by ECG, along with cardiotocography (CTG), results in fewer blood samples being taken from the baby's scalp, less surgical assistance and better oxygen levels at birth than CTG alone.
What action is necessary if a cardiotocography is suspicious or pathological?
- 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 blood pressure (BP) and consider 500 ml 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 bedpan 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 500 ml infusion of crystalloid if there are no contra-indications to this.
- If fetal blood sampling is indicated/feasible:
- Encourage the mother to use the left lateral position and check BP, giving 500 ml crystalloid if appropriate.
- Proceed to fetal blood sampling with maternal consent.
- Decide further course on the basis of fetal blood sampling results (see interpretation of fetal blood pH sampling below).
- If fetal blood sampling is not indicated or not feasible:
- Use left lateral position 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.
- The 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.
Interpretation of fetal blood pH sampling
Current NICE and RCOG guidance on appropriate responses to fetal scalp pH results is below:
- pH ≥7.25 - repeat fetal blood sample (FBS) if cardiotocography (CTG) abnormalities persist.
- pH 7.21-7.24 - repeat FBS within 30 minutes or consider delivery if there has been a rapid fall in pH since the last sample.
- pH ≤7.20 - delivery is 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
- A Swedish randomised controlled trial (RCT) examined the effectiveness of pH analysis of fetal scalp blood compared with lactate analysis in identifying hypoxia in labour to prevent acidaemia at birth. Most outcome measures showed NO statistical difference, eg acidaemia rate at birth, Apgar score; however, the large difference was in the rate of failure of obtaining a sample - much less with lactate (a smaller sample required) than pH.
- Vibroacoustic stimulation of the fetus as an adjunct to cardiotocography (CTG) may improve its utility by reducing the incidence of nonreactivity (if, for example, the fetus is sleeping). However, a recent Cochrane systematic review found that there is insufficient evidence from RCTs on which to base recommendations for use of vibroacoustic stimulation in the evaluation of fetal wellbeing in labour in the presence of a non-reassuring cardiotocographic trace.
- A new method of fetal pulse oximetry may be useful for reducing Caesarean section rates in the presence of non-reassuring CTG findings.
- 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.
- The combination of auto-analysis of fetal pulse oximetry and CTG data is also being investigated with some evidence of usefulness.
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 RCTs to optimise its utility and help improve and develop guidelines for its use.
Further reading & references
- Abdel-Hamid HZ et al, Cerebral Palsy, Medscape, Dec 2011
- Keogh JM, Badawi N; The origins of cerebral palsy. Curr Opin Neurol. 2006 Apr;19(2):129-34.
- Blair E, Watson L; Epidemiology of cerebral palsy. Semin Fetal Neonatal Med. 2006 Apr;11(2):117-25. Epub 2005 Dec 9.
- Vincer MJ, Allen AC, Joseph KS, et al; Increasing prevalence of cerebral palsy among very preterm infants: a population-based study. Pediatrics. 2006 Dec;118(6):e1621-6. Epub 2006 Oct 30.
- 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.
- Grivell RM, Alfirevic Z, Gyte GM, et al; Antenatal cardiotocography for fetal assessment. Cochrane Database Syst Rev. 2010 Jan 20;(1):CD007863.
- Kitzinger S, Green JM, Chalmers B, et al; Why do women go along with this stuff? Birth. 2006 Jun;33(2):154-8.
- Intrapartum care, NICE Clinical Guideline (2007)
- Alfirevic Z, Devane D, Gyte GM; Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev. 2006 Jul 19;3:CD006066.
- van Geijn H; Cardiotocography, ObGyn.net, 1998; An objective overview of the use of cardiotocography from a practising obstetrician
- Neilson JP; Fetal electrocardiogram (ECG) for fetal monitoring during labour. Cochrane Database Syst Rev. 2006 Jul 19;3:CD000116.
- 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.
- 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.
- Wiberg-Itzel E, Lipponer C, Norman M, et al; Determination of pH or lactate in fetal scalp blood in management of intrapartum fetal distress: randomised controlled multicentre trial. BMJ. 2008 Jun 7;336(7656):1284-7. Epub 2008 May 25.
- Tan KH, Smyth R; Fetal vibroacoustic stimulation for facilitation of tests of fetal wellbeing. Cochrane Database Syst Rev. 2001;(1):CD002963.
- 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.
- East CE, Chan FY, Colditz PB, et al; Fetal pulse oximetry for fetal assessment in labour. Cochrane Database Syst Rev. 2007 Apr 18;(2):CD004075.
- 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.
- 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.
|Original Author: Dr Sean Kavanagh||Current Version: Dr Hayley Willacy|
|Last Checked: 20/12/2010||Document ID: 1063 Version: 23||© EMIS|
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