Intrapartum fetal surveillance

Review

Intrapartum fetal surveillance

improved fetal monitoring in labour, failure to identify abnormal FHR patterns and lack of appropriate action are considered to be significant contributing factors. Soaring litigation and associated costs make the prospect of a career in obstetrics unattractive for many medical professionals. Historically, FHR monitoring has been used to assess the wellbeing of the fetus during labour. In most maternity units in the UK, monitoring of low risk labour is performed by auscultation of the FHR whilst cardiotocograph (CTG), fetal electrocardiogram (ECG) analysis and/or assessment of fetal acid base or lactate is used for high risk labour. Women are encouraged to make informed decisions together with their obstetrician, GP or midwife about intrapartum fetal surveillance based on accurate information and consideration of particular risk factors. There should be a clear communication with the individual woman in labour and the healthcare professionals. A clear consistent terminology to describe the FHR patterns should reduce errors in interpretation and management.

Sarala Premila Sabaratnam Arulkumaran

Abstract The course of labour is one of the most hazardous journeys one ever undertakes. The uterine contraction of labour subjects the fetus to a possible risk of hypoxic injury due to repeated cord compression or reduction of retro-placental perfusion. If the hypoxia is prolonged and/or severe, babies are at risk of either being born with a disability (physical or mental) or of dying during labour. Detection of fetal compromise should be followed by appropriate and timely intervention to reduce the incidence of intrapartum fetal deaths and neurological sequel related to birth asphyxia. Neonates who develop grade II or III hypoxic ischaemic encephalopathy due to birth asphyxia have a high risk of death or neurological sequel (up to 50%) that leads to major motor cognitive impairment (i.e. cerebral palsy). This article will discuss the principles of intrapartum fetal surveillance and highlight the areas of shortfall, and suggest actions that could be pursued to reduce avoidable morbidity and mortality.

Methods of intrapartum fetal monitoring Intermittent auscultation This is a non-continuous method of listening to the FHR at predetermined intervals during labour, either by a Pinard stethoscope, a hand-held Doppler ultrasound device or intermittent electronic fetal monitoring (EFM). Intermittent auscultation (IA) is recommended as a minimum for women who, at the onset of labour, are identified as low risk of developing fetal ­compromise. One randomized controlled trial (RCT) comparing the methods of intermittent monitoring concluded that there was a significant increase in the caesarean section rate when FHR was monitored with either intermittent EFM or a hand-held Doppler device. Although there is a lack of empirical evidence on the optimal frequency of IA, the following recommendations were made by the National Institute of Clinical Excellence (NICE):

Keywords birth asphyxia; electronic fetal monitoring; encephalopathy; fetal surveillance; hypoxia

Introduction The 4th Confidential Enquiry into Stillbirths and Deaths in Infancy that reviewed intrapartum mortality of the fetus weighing >1500 g with no chromosomal or congenital malformation revealed it to be 1 in 1600 in 1995. In the UK the incidence of hypoxic ischaemic encephalopathy (HIE) grades I–III is about 2–3 in 1000 whilst of grades II and III it is about 1 in 1000. In 2007 the NHS Litigation Authority (NHSLA) estimated potential liabilities of £3.7 billion related to clinical negligence in obstetrics. Although the cause for most cases of cerebral palsy is unknown, obstetricians are often held responsible for adverse outcome attributed to intrapartum asphyxia as evidenced by fetal heart rate (FHR) abnormalities, meconium staining, low Apgar score, umbilical cord blood acidosis and neonatal encephalopathy. However, many of these surrogate markers have limitations in identifying the timing of hypoxic injury and are a frequent cause of controversy in the determination of causation, preventability and liability. Although most perinatal morbidity and mortality may not be prevented by

‘FHR should be auscultated every 15 minutes for duration of one minute soon after a contraction during the first stage of labour and every 5 minutes or after every other contraction during the second stage of labour. The maternal pulse should be palpated and the fetal heart rate auscultated to differentiate between maternal and fetal heart rate. The uterine contractions should be palpated and the frequency and duration of contractions noted. IA should be practised by experienced practitioners. There should be defined clinical interventions when non re-assuring findings are present.’

Sarala Premila MSc MRCOG is a Specialist in Obstetrics and Gynaecology at St George’s Hospital, Blackshaw Road, London, UK.

The Cochrane systematic review comparing RCTs of IA and continuous EFM for low-risk women in labour suggested that the only clinical significant benefit from the use of routine continuous EFM monitoring was in the reduction of neonatal seizures, whilst it increased the caesarean section and operative vaginal delivery rates.

Sabaratnam Arulkumaran FRCS FRCOG PhD MD is Professor and Head of Department of Obstetrics and Gynaecology, St George’s Hospital, Blackshaw Road, London, UK.

Continuous electronic fetal monitoring This is the most widely used method of intrapartum fetal surveillance in high-risk labour. This is achieved by using a Doppler

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ultrasound transducer placed on the mother’s abdomen (external CTG) or a scalp electrode (internal CTG) to monitor the baby’s heart rate. A pressure gauge transducer is placed on the abdomen between the uterine fundus and the umbilicus to monitor uterine contractions. CTG is a continuous recording of the fetal heart rate combined with a recording of uterine activity. The 4th Confidential Enquiry into Stillbirths and Death in Infancy Report (CESDI, 1997) highlighted the recurring problems related to incorrect interpretations of intrapartum FHR tracings. Avoidance of morbidity and mortality could be achieved only by having protocols for appropriate interpretations, adequate communication of the findings and timely clinical response for a suspicious or pathological CTG. The clinical picture needed to be considered to take appropriate action based on the CTG. Since the introduction of EFM, there are growing allegations of obstetric malpractice based on the failure to perform prompt delivery in the presence of abnormal FHR patterns. To minimize errors in interpretation, the Royal College of Obstetrician and Gynecologists (RCOG) recommends that the settings on CTG machines should be standardized so that the paper speed is 1 cm/min; sensitivity displays are 20 bpm/cm and the FHR range displays are 50–210 bpm. The patient’s name, hospital number, date of birth, date and time of the recording, pulse rate and temperature should always be checked and recorded before starting actual recording. The FHR should be auscultated by a Pinard’s stethoscope or a Doppler device before commencing EFM to avoid the maternal pulse being recorded by the fetal monitor. Ideally both tocograph and cardiograph tracings should be clearly recorded in a continuous manner, i.e. a technically satisfactory trace. All intrapartum events (i.e. vaginal examination, fetal blood sample, epidural, mode of delivery) should be noted on the CTG. CTGs should be kept for a minimum of 25 years and therefore adequate provisions should be available for their secure storage and easy retrieval. Some hospitals in the UK incorporate central fetal monitoring into labour and delivery suites. This allows FHR patterns from different labouring women to be viewed simultaneously. This allows input from colleagues and senior personal and may provide a higher level of vigilance leading to a better perinatal outcome (similar to ‘neighborhood watch’). The system also avoids medical personal walking too often into rooms to review CTGs which disturbs the privacy of the woman and her partner. However, the impact of such a system needs to be studied further as a study by Weiss et al concluded that central fetal monitoring did not improve perinatal outcome but did increase the caesarean section rate. In high-risk women where continuous EFM is recommended in labour, if the EFM is normal, monitoring may be interrupted for short periods of up to 15 min to allow personal care (shower, toilet). These interruptions should not occur immediately after any intervention that might be expected to alter FHR (e.g. amniotomy, epidural insertion or top up, or whilst on oxytocin infusion). Indications for the use of continuous EFM are listed in Table 1.

Indications for the use of continuous electronic fetal monitoring Maternal problems • Previous caesarean section • Hypertension • Post-term pregnancy (>42 weeks) • Prolonged rupture of membranes (>24 h) • Induced labour • Diabetes • Antepartum haemorrhage (placental abruption) • Medical disorders such as systemic lupus erythematosus Fetal problems • Fetal growth restriction • Prematurity • Oligohydramnios • Abnormal Doppler artery velocimetry • Multiple pregnancy • Meconium stained liquor • Intrauterine infection Intrapartum risk factors • Oxytocin augmentation • Epidural analgesia • Vaginal bleeding in labour • Maternal pyrexia • Fresh meconium stained liquor Table 1

evidence that the admission CTG in low-risk pregnancies confers any significant benefits in perinatal outcome. It is associated with an increase in the continuous use of EFM, augmentation of labour, epidural analgesia and operative delivery. Despite lack of evidence, the admission test followed by continuous EFM is practised in several units in the UK in low-risk labour and is probably linked to lack of staff to perform one-to-one care and auscultation every 15 min.

Interpretation of the CTG FHR pattern recognition should be in relationship to the uterine contractions. The four features of the heart rate – the baseline rate, baseline variability, accelerations and decelerations – should be described. The features of CTGs need to be defined when describing a trace. The terminology used in describing these features is given in Table 2. After defining the individual features, the CTG trace needs to be classified as normal, suspicious or abnormal (Table 3). Based on the contribution of all the features, the whole CTG is classified as normal, suspicious or pathological (Table 4). A normal CTG is associated with a low probability of fetal compromise and has the following features: baseline rate 110– 160; baseline variability of 5–25 bpm; accelerations of 15 bpm for 15 s; no decelerations. A poor outcome despite a normal CTG (false negative) may be due to maternal (pyrexia, intrauterine infection) or fetal (congenital or metabolic) problems.

Admission CTG The admission CTG is a screening test which is used in most units on admission to the delivery suite, and aims to identify the fetus at increased risk of intrapartum hypoxia. There is no

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Definitions and descriptions of individual features of fetal heart trace Term

Definition

Baseline fetal heart rate (FHR)

The mean FHR when this is stable, excluding accelerations and decelerations. It is determined over a period of 5–10 min and expressed in beats/min (bpm) 110–160 bpm 100–109 bpm 161–180 bpm <100 bpm >180 bpm Minor fluctuations in baseline FHR occurring at 3–5 cycles/min. It is measured by estimating the difference in bpm between highest peak and lowest trough of fluctuation in a 1-min segment of the trace ≥5 bpm between contractions <5 bpm for 40 min or more but <90 min <5 bpm for 90 min or more Transient increase in FHR of 15 bpm or more and lasting 15 s or more Transient episodes of slowing of FHR below the baseline level of >15 bpm and lasting 15 s or more Uniform, repetitive, periodic slowing of FHR with onset early in the contraction and return to baseline at end of contraction Uniform, repetitive, periodic slowing of FHR with onset mid to end of contraction and nadir >20 s after the peak of the contraction and ending after the contraction. In the presence of a non-accelerative trace with baseline variability <5 bpm the definition would include decelerations of <15 bpm Variable, intermittent, periodic slowing of FHR with rapid onset and recovery. Time relationships with contraction cycles are variable and they may occur in isolation An abrupt decrease in FHR <80 bpm. It is suspicious if it is <3 min and is pathological if it is >3 min

Normal baseline FHR Moderate bradycardia Moderate tachycardia Abnormal bradycardia Abnormal tachycardia Baseline variability Normal baseline variability Non-reassuring baseline variability Abnormal baseline variability Accelerations Decelerations Early decelerations Late decelerations

Variable decelerations Prolonged decelerations Sinusoidal pattern

A regular oscillation of the baseline long-term variability resembling a sine wave. This smooth, undulating pattern, lasting at least 10 min, has a relatively fixed period of 3–5 cycles/min and amplitude of 5–15 bpm above and below the baseline

Reproduced from the NICE/RCOG guidelines.

Table 2

­ ompliance with guidelines and documentation with contempoC raneous records is good practice. All CTGs considered as suspicious or pathological by this definition require further evaluation, taking into account the full

clinical picture. The RCOG has developed algorithms to guide obstetricians and midwives in the management of abnormal FHR patterns. However, variations in the interpretation of CTG tracings result in false reassurance and lack of appropriate ­intervention.

Classification of fetal heart rate features according to the National Institute of Clinical Excellence (NICE) Feature

Baseline rate (bpm)

Variability

Decelerations

Accelerations

Reassuring

110–160

≥5

None

Present

Non-reassuring

100–109

<5 for >40 min but <90 min

Early decelerations

The absence of accelerations with an otherwise normal CTG is of uncertain significance

161–180

Abnormal

<100 >180 Sinusoidal pattern for >10 min

Variable decelerations Single prolonged deceleration <80 bpm for up to 3 min <5 for ≥90 min

Atypical variable decelerations Late decelerations Single prolonged deceleration <80 bpm for >3 min

Table 3

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Pre-terminal CTGs Loss of variability and shallow decelerations in a non-reactive trace The CTG that shows a total loss of variability with shallow decelerations is suggestive of a hypoxic fetus and neurological damage may have occurred in some of the babies (Figure 1). Immediate delivery should be undertaken in such situations and a delay in intervention in the presence of uterine contractions may aggravate existing hypoxia, leading to more hypoxia and acidosis and its sequel. Usually there is evidence of clinical compromise such as intrauterine growth retardation, bleeding, infection, meconium, absent fetal movements (FM) or prolonged pregnancy.

Classification of CTG according to NICE guidelines Category

Definition

Normal

A CTG where all four features fall into the ‘reassuring’ category A CTG where one of the features falls into the ‘non-reassuring category’ and the remainder of the features are reassuring A CTG whose features fall into two or more non-reassuring categories or one or more abnormal categories

Suspicious

Pathological

Prolonged decelerations <80 bpm for >3 min Prolonged decelerations <80 bpm for >3 min require urgent intervention. Abruption, cord prolapse and caesarean scar rupture warrant immediate delivery. In the absence of these, if the heart rate does not show signs of recovery towards the normal baseline rate by 6 min, the ‘3, 6, 9, 12 and 15’ minute guidance may be used. Interventions like stopping syntocinon infusion, maternal ­positioning, hydration and tocolysis when required should be instituted whilst awaiting recovery by 6 min. If the CTG remains pathological, the mother should be moved to the operating theatre by 9 min. Caesarean section should be commenced by 12 min with the aim of delivering the fetus by 15 min. Although the vast ­majority of CTGs with prolonged decelerations are likely to recover by 9 min, abnormal CTGs with tachycardia, reduced baseline ­variability and decelerations prior to bradycardia have less likelihood of recovery and a greater chance of poor outcome. If operative vaginal delivery is feasible the fetus should be ­delivered within 20 min. A difficult instrumental delivery should be avoided.

Table 4

Nelson et al reported that the specificity of the CTG for prediction of cerebral palsy is low, with a reported false-­positive rate as high as 99.8% even in the presence of multiple late decelerations or decreased variability. The following features are unlikely to be associated with significant fetal compromise when they occur in isolation. • Baseline rate 100–109 bpm; • Absence of accelerations; • Early decelerations; • Variable decelerations without complicating features. Fetal compromise in labour may be due to a variety of pathology, including placental insufficiency, uterine ­hyperstimulation, maternal hypotension, cord compression and placental abruption. Identification of any reversible cause of abnormality and initiation of appropriate action (correction of maternal hypotension, cessation of oxytocin and/or tocolysis for excess of uterine activity) has been shown to be useful to correct FHR ­abnormality. The following features may be associated with fetal compromise and the chances are greater with increasing number of abnormal features: • Fetal tachycardia >160 bpm; • Reduced baseline variability <5 bpm for >90 min; • Complicated or atypical variable decelerations; • Late decelerations; • Prolonged decelerations <80 bpm for >3 min; compromise increases with duration, low heart rate, reduced/absent variability and clinical conditions of abruption or scar rupture. The healthy fetus has many special physiological mechanisms to protect it from recurrent transient mild hypoxic episodes that can occur during labour. An intrapartum hypoxic event can be silent. It is only when it is apparent or detectable that it helps to define the probable timing of the event and the determination of whether its sequelae might have been preventable. It is not always possible to ascertain retrospectively whether an intervention could have prevented cerebral damage in any individual case where no detectable sentinel hypoxic event has occurred. The actual duration and degree of hypoxia required to produce cerebral palsy in a healthy fetus is variable. It is easy to recognize a normal CTG and a pre-terminal CTG. Taking action based on a suspicious and/or a pathological CTG with one or two abnormal features has always been a challenge in obstetrics.

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Continuous EFM is sensitive in the detection of fetal hypox­ aemia and acidaemia but the specificity is low. To improve the specificity of EFM the following adjuvant tests of fetal wellbeing are in use. Fetal scalp blood sampling Fetal blood sampling (FBS) is a well established adjunct to EFM but is an invasive procedure. A sample of blood is taken from the fetal

Figure 1 A pre-terminal trace with no accelerations, markedly reduced baseline variability and shallow late decelerations.

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scalp using an amnioscope and is subjected to blood gas analysis. The test has its short comings: it can be difficult to perform at cervical dilatation <3 cm; skill is required to ensure a good quality sample; and the procedure may be stressful and appear as an unnecessary intervention to the mother. Contraindications for FBS include maternal infections such as HIV, hepatitis B or C, herpes, fetal bleeding disorders such as haemophilia and premature gestation (<34 weeks). FBS immediately after prolonged deceleration can show respiratory acidosis which corrects itself with recovery of the FHR and hence in such situations it is an unnecessary intervention. Repeated samples at reasonable time intervals need to be taken to establish a trend. FBS is performed only when a CTG is not reassuring despite corrective measures of positioning, stopping oxytocin infusion and hydration. FBS results should be interpreted in the context of the clinical situation which includes parity, progress of labour and clinical features of both the mother and fetus. FBS is complimentary to EFM in the detection of fetal compromise and to help in deciding more precisely as to when to assist delivery. Normal and abnormal values of pH and base excess are shown in Table 5. If pH is <7.20, immediate delivery is indicated. If the FBS is within the normal range (pH > 7.25) it reassures the clinician but in the presence of CTG abnormalities a repeat FBS is suggested after a suitable interval. A value of 7.20–7.24 warrants a repeat FBS within 30 min. In cases of confirmed fetal compromise (rapidly falling fetal scalp pH or pH < 7.20) delivery should be accomplished within 30 min. It is recommended that umbilical arterial and venous blood should be collected at the time of delivery to confirm acid base status when an intrapartum FBS has been performed. Studies have shown that the use of FBS in conjunction with EFM is associated with a decrease in operative delivery rates compared with EFM alone.

oxygenated haemoglobin absorb light at different wavelengths and by using standard curves the oximeter is able to determine the fetal oxygen saturation. The pulse oximeter requires a probe which is inserted transcervically and placed against the fetus. The probe is connected to a conventional heart rate monitor that displays a signal of continuous fetal oxygen saturation. Although normal oxygen saturation measurements support fetal wellbeing, there is insufficient data available to recommend its routine use. Fetal electrocardiogram ST waveform analysis In recent years, the fetal ECG has been used as an additional test of fetal wellbeing. The fetal ECG is recorded continuously from a scalp electrode and analysed using computer technology. Hypoxaemia during labour can alter the shape of the fetal ECG waveform, particularly the elevation or depression of the ST segment. Clinical trials suggest that the use of ST waveform analysis has helped in the reduction in operative deliveries for suspected fetal compromise and the incidence of metabolic acidosis. Results from some centres are not encouraging, possibly due to the dependence of this method on interpretation of CTG when an ECG abnormality is detected. Further RCTs are likely to clarify its use in intrapartum surveillance. Fetal stimulation tests The use of a fetal acoustic stimulation test (FAST) has been reported to predict an acidotic fetal pH. An artificial electronic larynx is used near the region of the fetal head to startle and wake up the fetus, whereupon the fetus exhibits movements and heart rate accelerations. If accelerations are noted in the CTG after the test, a fetal pH of <7.2 is unlikely. If the FAST test is negative, delivery should be considered in situations where it is not feasible to perform additional tests of fetal wellbeing.

Fetal scalp lactate measurement Intrapartum fetal hypoxia can lead to accumulation of lactic acid in the fetus and blood lactate levels may be used as an indicator of fetal acidosis. This invasive procedure is similar to FBS, but the lactate measurements require 5 μl of blood compared with 35 μl needed for pH and base excess determination. Available data indicate that fetal scalp lactate levels of 2.9–3.08 mmol/L should be considered suspicious and levels >3.08 mmol are abnormal and need immediate intervention. Lactate measurement is used in place of pH measurements in some centres.

Conclusion EFM was introduced 30 years ago with the hope of reducing intrapartum deaths and fetal morbidity. Decades later, however, the results are not too convincing and, in spite of a nearly universal use, there has been no reduction in the incidence of cerebral palsy. Despite questions about its efficacy and outcomes associated with its use, FHR monitoring continues to be the predominant method for intrapartum fetal surveillance. A large proportion of asphyxial damage begins before labour and may not benefit from EFM-prompted intervention during labour. The challenge of intrapartum fetal surveillance is to identify those few fetuses who are about to be compromised and to intervene before injury occurs. However, not all intrapartum adversities can be avoided despite intensive surveillance and the increasing high rate of interventions. ◆

Fetal pulse oximetry Fetal pulse oximetry aims to provide a continuous assessment of fetal oxygen saturation. Pulse oximetry relies on the detection of arterial pulsation for the measurement of oxygen saturation. This modality is based on the principle that deoxygenated and

Normal and abnormal values of pH and base excess pH

Base excess

Normal: >7.25 Suspicious: 7.20–7.24 Abnormal: <7.20

Normal: <−8 mmol/L

Further reading Amer-Wahlin I, Hellsten C, Noren H, et al. Cardiotocography only versus cardiotocography plus ST analysis of fetal electrocardiogram for intrapartum fetal monitoring: a Swedish randomized controlled trial. Lancet 2001; 358: 534–538. (A trial of 4966 women, demonstrating the potential of ST analysis in labour to prevent unnecessary operative deliveries with improvement of perinatal outcome).

>−12 mmol/L

Table 5

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Badawi N, Kurinczuk JJ, Keogh JM, et al. Antepartum risk factors for newborn encephalopathy: the Western Australia case-control study. BMJ 1998; 317: 1549–1553. Badawi N, Kurinczuk JJ, Keogh JM, et al. Intrapartum risk factors for newborn encephalopathy: the Western Australian case-control study. BMJ 1999; 317: 1554–1558. Low JA. Intrapartum fetal surveillance. Is it worthwhile? Obstet Gynecol Clin North Am 1999; 26: 725–739. Maternal and Child Health Research Consortium. Confidential Enquiry into Stillbirths and Deaths in Infancy. 4th Annual Report. Concentrating on intrapartum related deaths 1994–1995. www.cemach.org.uk Neilson JP, Mistry RT. Fetal electrocardiogram plus heart rate recording for fetal monitoring during labour (Cochrane review). Cochrane Library 2002; Issue 4. (A meta-analysis identifying well-performed clinical trials on fetal electrocardiogram monitoring). Nelson KB, Dambrosia JM, Ting TY, et al. Uncertain value of electronic fetal heart rate monitoring in predicting cerebral palsy. N Engl J Med 1996; 334: 613–618. Royal College of Obstetricians and Gynaecologists. The use and interpretation of CTG in intrapartum fetal surveillance (2001). Evidence-Based Clinical Guideline No. 8. London: RCOG Press, 2001.

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Thacker SB, Stroup D, Chang M. Continuous electronic heart-rate monitoring for fetal assessment during labour (Cochrane review). Cochrane Library 2002; Issue 4. Weiss PM, Balducci J, Reed J, Klasko SK, Rust OA. Does centralized monitoring affect perinatal outcome? J Matern-Fetal Med 1997; 6: 317–319. Williams B, Arulkumaran S. Cardiotocograph and medico legal issues. Best Pract Res Clin Obstet Gynaecol 2004; 18: 457–466.

Practice points • Concise, accurate and contemporaneous documentation of intrapartum events is essential for management • The methods of intrapartum fetal surveillance and decision to intervene should be based on the clinical situation • The knowledge to interpret CTGs and to take appropriate actions needs to be improved by regular multidisciplinary learning • Each unit should have regular audits to evaluate the clinical outcome in relation to CTGs with the aim to improve outcome

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