Cardiotocography: An Introduction

This article originally appeared in the AvMA Lawyers Service Newsletter (June 2018)

Cardiotocography traces form a central piece of documentary evidence in litigation related to adverse perinatal outcomes, which are alleged to have arisen due to events that took place during the labour and/or delivery of the baby. Cardiotocography is therefore an important element to get to grips with for any practitioner when working on birth injury cases. Errors in electronic‏ fetal heart rate monitoring or cardiotocography are a‏ common theme in such cases with injuries to the baby‏ including cerebral palsy, stillbirth and scarring and injuries‏ to the mother including damage to the mother’s perineum‏ or vagina resulting in disability which limits sexual‏ intercourse, lack of control of bladder/bowel function‏ and of course psychological or psychiatric sequelae.‏ A recent review by NHS Resolution in September 2017‏ found that 32 out of the 50 cerebral palsy cases looked‏ at, involved errors of cardiotocography interpretation.‏ This article is a beginner’s guide to cardiotocography for‏ application in medical negligence cases.‏ ‏

What is cardiotocography?‏

Cardiotocography is a technical means of recording‏ the fetal heartbeat and the uterine contractions during‏ pregnancy and intrapartum. The cardiotocography‏ recording is produced in the form of a graphical trace‏ and is important to midwives and obstetricians when‏ evaluating in real time whether there is fetal compromise‏ or not. The upper channel [cardiograph] represents‏ the fetal heart and the lower [tocograph] records the‏ frequency of uterine contractions [not strength].‏ ‏ The cardiograph may be recorded by an ultrasound signal‏ through the mother’s abdominal wall or via an electrode‏ attached to the baby’s scalp, so called a fetal scalp‏ electrode. The tocograph is produced by an external‏ tocodynamometer placed at the fundus of the uterus to‏ measure the frequency of the contractions.‏ Internal monitoring of the fetal heart rate by use of a fetal‏ scalp electrode provides a more accurate and consistent‏ transmission of the fetal heart rate than external‏ monitoring because factors such as movement do not‏ affect it. Internal monitoring may be used when external‏ monitoring of the fetal heart rate is inadequate, or closer‏ surveillance is needed.‏ The current relevant guidance on cardiotocography‏ is detailed within NICE Clinical Guideline CG190 on‏ Intrapartum Care[1] . The use of a standard format in the‏ guidance to interpret and respond to fetal heart rate,‏ serves to facilitate safety in clinical practice and provide‏ more clarity in legal cases. Practitioners should refer to‏ the relevant guidance in place at the time of the alleged‏ negligence when considering matters of negligence.‏ More about the guidance below.‏ ‏

Usage

Cardiotocography is most commonly used in the third‏ trimester and during labour. Its purpose is to monitor‏ fetal wellbeing and allow detection of fetal distress which‏ usually means the fetus is hypoxic or anoxic. [deprivation‏ of adequate oxygen supply]. All pregnancies, regardless of‏ risk category, need effective monitoring: only 1 in 5 claims‏ for cardiotocography interpretation‏ involve a high-risk pregnancy[2]. An‏ abnormal CTG trace indicates the‏ need for more invasive investigations‏ and potentially emergency Caesarean‏ ‏ section. Appropriate interpretation of CTG traces is‏ therefore fundamental if there is to be a reduction in‏ the number of baby deaths and/or serious injury. The‏ relevance to medical negligence work will be patently‏ clear.

Interpretation

Interpretation of CTG traces is a very complex subject of‏ which experts frequently differ. As a consequence, even‏ the most superficial review would be beyond the scope‏ of this article.‏

Lawyers are advised to leave the interpretation of CTG‏ traces to their instructed experts. Experts will be looking at‏ the traces when considering the standard of care provided‏ and whether there were signs of fetal compromise or not‏ at a certain time which should have prompted earlier or‏ later action in relation to delivery. Below is only a highlevel‏ summary of the main features.

Tables 10 and 11 of the current NICE guideline, CG190‏ provide guidance on the interpretation of CTG traces‏ and the reader is referred to the whole of section 10 for‏ further information.[3]‏

The four main features used to assess a CTG trace are:‏

1. Baseline fetal heart rate
2. Baseline variability
3. Fetal heart rate acceleration
4. Fetal heart rate decelerations‏ ‏

Generally, accelerations are a sign the baby is healthy.‏ The appropriate response to a uterine contraction is an‏ increase in the fetal heart rate [acceleration]. The baseline‏ rate is the average heart rate of the fetus in a 10-minute‏ window. The normal fetal heart rate is between 110 –‏ 150bpm. A baseline variation of less than 5 bpm is an‏ abnormal sign! Variability greater than 5bpm is generally‏ a sign that the baby is healthy.

Decelerations are an abrupt decrease in the baseline fetal‏ heart rate by 15 bpm for 15 seconds or more. There are‏ different kinds of decelerations, [early, variable, late and‏ prolonged] each with varying significance. The baseline‏ rate, variability and decelerations are categorised as‏ ‏ normal/reassuring, non-reassuring and abnormal as per‏ Table 10. Table 11 provides the management approach‏ subject to the interpretation and categorisation of‏ the features of the CTG trace. When there is a single‏ prolonged deceleration or bradycardia with a baseline‏ below 100 bpm persisting for 3 minutes or more, the CTG‏ is classed as abnormal and warrants the need for urgent‏ intervention.‏

When instructing experts, practitioners should ensure that‏ the full clinical picture is taken into account, as clinicians‏ must do in practice. Such factors include the presence‏ of meconium stained liquor in the amniotic fluid; delay‏ during labour[4], abnormal fetal position and whether there‏ is acidosis following blood gas analysis of a fetal blood‏ sample. Furthermore, whether the pregnancy was high or‏ low risk will also be relevant. Such factors will assist when‏ trying to understand what the picture was at the time of‏ the index events and what the clinicians knew at that time‏ when providing treatment and care.‏

Medical negligence

Uncertainty is part and parcel of CTG traces and therefore‏ the scope for error can make clinical negligence claims‏ challenging. Traces have a high false positive rate and the‏ transducer could be picking up the maternal heart rate‏ instead of the fetal heart rate. Practitioners should try and‏ draw out any potentially misleading features on the CTG‏ traces with their experts in order to get a realistic snapshot‏ of how a responsible body would have interpreted the‏ CTG trace at the time. Intrauterine observation along‏ with consideration of the full clinical picture is critical in‏ determining whether or not breach of duty is established.‏ The majority of birth injury cases incorporate similar‏ allegations of negligence which broadly centre around‏ the inability to interpret the CTG trace correctly, for‏ example failure to identify bradycardia in time leading to‏ delay in proceeding to caesarean section. In the ordinary‏ case it is still necessary to show that the signs of foetal‏ compromise could reasonably have been detected and‏ that delivery could and should have been expedited.‏ Casework will usually include analysis of the timings as‏ to when fetal distress would have been identified by a‏ reasonably competent midwife/obstetrician and at what‏ time should certain steps/treatment have taken place.‏ Conversely allegations relating to liability may be that the‏ delivery was carried out too soon causing injury.‏

In the event breach of duty can be proved by a Claimant, it‏ will still be necessary for the Claimant to prove on balance‏ that the injury, be it cerebral palsy or otherwise would have been avoided if delivery was expedited at a certain‏ time. Not only can breach of duty be a difficult hurdle to‏ overcome in obstetric cases, but causation can also bring‏ its challenges. The experts will need to consider what‏ would have happened if the patient had been delivered at‏ a certain time with appropriate management along with‏ the likely cause of the injury actually suffered. In cerebral‏ palsy cases, paediatric neurology expert evidence may be‏ needed to identify the cause of brain damage which may‏ have occurred in any event irrespective of any delay.‏

Practical guidance‏

The doctor’s or midwife’s clinical notes are not sufficient;‏ practitioners must consider the CTG traces themselves.‏ Claimant lawyers will need to ensure they have the whole‏ trace relating to the labour and delivery of the baby in‏ any given case and that it is clear enough to be read.‏ Practitioners should instruct their experts [obstetricians or‏ midwives] to explain the trace in detail in their reports with‏ reference to the relevant guidance in place at the time‏ of the index events. Similarly, the Defendant clinicians’‏ witness statements in relation to the interpretation of the‏ CTG trace must be cross referenced with the Claimant’s‏ expert’s own interpretation of the trace. When preparing‏ for trial, parties may wish to include a glossary of terms‏ in the trial bundle to assist the Court with the technical‏ medical concepts and practitioners should also consider‏ enlarging the traces for trial in order to ensure they are as‏ legible as possible reducing the scope for error.‏

Finally, cardiotocography despite its limitations and‏ scope for error is here for the foreseeable future. There‏ is not currently a more effective way of monitoring fetal‏ wellbeing and therefore doctors, nurses and lawyers will‏ need to continue to rely upon them and endeavour to‏ interpret them.‏