Intrapartum 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 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' 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:^1,2

• 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.³
• 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.⁴
• 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 (odds ratio 2.85, 95% confidence interval 0.99 to 7.12).⁵
• The widespread use of electronic fetal monitoring as part of the management of normal labour has been discarded, as a result of professional and lay voices alike.^6,7
• 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.⁸

• 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

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.

• 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 to urgently 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.

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.⁷ The lists are not exhaustive and other risk factors may prompt the use of continuous monitoring.

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

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

• A Swedish 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 e.g. acidaemia rate at birth, APGAR score, but the large difference was in the rate of failure of obtaining a sample - much less with lactate (smaller sample required) than pH.¹³
• 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).¹⁴ 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.¹⁵
• A new method of fetal pulse oximetry may be useful for reducing caesarean section rates in the presence of non-reassuring CTG findings.¹⁶
• 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.¹⁷
• The combination of auto-analysis of fetal pulse oximetry and CTG data is also being investigated with some evidence of usefulness.¹⁸

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.