Physiology-based interpretation of CTG reflects a journey back to the very foundation of clinical medicine taught in the first few years of medical school. This includes taking a good history, performing relevant clinical examination and investigations to arrive at a diagnosis (or a differential diagnosis), and then formulating an individualized management plan based on the diagnosis. Obstetric and medical history is the most crucial aspect of physiological interpretation of CTG traces which would entail scrutiny of the CTG trace for specific features to ensure timely and appropriate interventions. Clinical examination is vital as derangements of the maternal environment (e.g. pyrexia, hypoxia, dehydration, ketoacidosis, hypotension, abruption) may result in specific fetal heart rate changes. Timely and appropriate management depends on the specific diagnosis, and this invidualization of care is the key principle of physiology-based CTG training and interpretation. Therefore, it differs from most CTG guidelines that treat all human fetuses the same by recommending the same management for ‘suspicious’ or ‘pathological’ CTG traces.

Healthcare provision involves humans (clinicians and non-clinicians) working in a complex environment consisting of equipment, technology, organizational culture and attitudes and behaviours of fellow team members as well as their patients and families. Human factors refer to the intricate link between knowledge, skills and competencies, the environment in which clinicians work, their personal circumstances, and the nature of communication between team members. Possession of individual knowledge, skills and competencies alone will not lead to the desired clinical outcomes if all other aspects of human factors are not understood and rectified. Pereira et al. identified 12 key aspects of human factors that may contribute to poor outcomes relating to CTG interpretation, based on ‘Du Pont’s dirty dozen’ from the airline industry. Addressing these key areas where ‘human factors’ is essential to optimize perinatal outcomes. Four consecutive ‘Each Baby Counts’ (EBC) Reports have reported that >50% of all cases of severe intrapartum hypoxia-related brain injury and perinatal deaths in the UK was due to CTG misinterpretation/fetal scalp blood sampling.

Risk refers to the likelihood (or probability) of an adverse event or harm, and risk management has been defined by the Australia/New Zealand standard as the culture, processes and structures that are directed towards realizing potential opportunities while managing adverse effects. The principles of risk management include risk identification, risk analysis, risk control and appropriate funding and resources to ensure corrective and preventive actions are developed and implemented to prevent future harm. NHS Resolution has reported that 49% of total clinical negligence cost of harm (£5.1 billion) in 2023/24 relates to maternity, which is approximately £2.5 billion per year or £6.84 million daily. It is essential to focus on prevention of avoidable harm while implementing risk management strategies to avoid poor outcomes. The main ‘root cause’ that could be identified in many of the cases of poor outcomes due to CTG misinterpretation is the use of illogical CTG guidelines which arbitrarily group different CTG categories, and then randomly combine them with unscientific time limits to arrive at an overall classification of CTG traces into ‘normal, suspicious, pathological’.

Obstetrics claims accounted for 62% of all clinical claims by value received in the year, highlighting the underlying impact of the financial costs of maternity indemnity payments, alongside the impact of harm on patients, families and healthcare staff. CTG misinterpretation contributes substantially to claims pertaining to mismanagement of labour and cerebral palsy. Medical negligence involves establishing causation and liability. Presence of abnormal CTG, low Apgar score, low cord arterial pH, assisted ventilation, admission to neonatal intensive care, moderate or severe neonatal encephalopathy and subsequent neurological damage point to asphyxia as a possible cause. However, several intrinsic fetal disorders cause neurological disability and an abnormal CTG may have been coincidental. Causation is best determined by neuroradiologist and paediatric neurologist based on the areas of scarring within the brain on MRI. The thalamus, basal ganglia injury show scarring, reflecting acute profound hypoxia while prolonged partial hypoxia results in bilateral cortical atrophy. Expert opinion is requested to judge whether the care provided fell short of what was expected (Bolam principle).

It is very much hoped that this book, which has moved away from the illogical, unscientific and potentially dangerous ‘nNormal, suspicious, pathological’ classification from its first publication in 2017, and is based on the principles of physiological interpretation of CTG, in line with the International Expert Consensus Statement published by more than 50 CTG experts from over 20 countries in 2024, will continue our journey to reduce avoidable harm to women, birthing people, their babies and the families. We owe this to women, birthing people, their babies and families who have placed in their trust in us to provide evidence-based clinical care, which is based on scientific foundations and the application of the knowledge of fetal pathophysiology.