Improving assessment of fetal health

LOUISE FRAMPTON reports.

Electronic monitoring of the baby’s heart beat is a well established way to diagnose fetal distress, either during or before labour. The method called cardiotocography (CTG) gives a print out of the baby’s heartbeat and associated uterine contractions. During labour, the stress of contractions and descent through the birth canal can reduce a baby’s oxygen supply. Most babies are able to cope with this stress, but around 2% suffer birth asphyxia.1 Some 250 babies in the UK die each year2 as a result of oxygen deprivation, while those who survive may suffer permanent brain damage. This article is about antepartum cardiotocography, which is used to measure a baby’s health before powerful labour contractions have begun. Before its introduction in the 1970s, the only way to assess fetal health before labour was through the mother’s perceptions of movements, listening to the fetal heartbeat with a stethoscope, or through an X-ray of the uterus. Today, the use of the antepartum CTG to monitor fetal heart beat and uterine contractions is standard practice across the world – providing a low cost method of detecting fetal distress before labour. It is effective in detecting the ‘terminal trace’ (when the heartbeat is flat with repetitive shallow decelerations).3 This is a rare and extreme situation. More commonly, with less severely affected babies, the abnormalities of the trace may be more subtle, which makes visual interpretation difficult. This raises the issue of how to interpret the many different heart rate patterns in the ‘grey area’ between what is clearly defined as ‘normal’ and what is grossly ‘abnormal’. Here, opinion on the meaning of a trace can vary significantly between clinical staff. Visual interpretation is always subjective to the extent that many studies confirm that even experienced observers frequently disagree with each other. Moreover, not all observers are experienced, which is an even greater problem and may lead to unnecessary intervention or, worse still, no intervention when it is urgently required. In fact, a large number of studies have identified the drawbacks of visual interpretation of the CTG .4-6 To overcome this problem, a system of computerised interpretation of the CTG is needed. One of the pioneers behind the Dawes Redman CTG computerised analysis system, Professor Chris Redman points out that visual assessment of the trace is still commonplace, despite the unresolved issue of unreliability and poor standardisation. “A visual assessment is a ‘guesstimate’ – this is simply not good enough,” he commented. “Any test that may lead to interventions that are not trivial and are involved with life and death should be based on reliable, reproducible and accurate measurement,” he argued. Clinical scoring systems have been introduced to attempt to standardise visual assessment .7 However, Prof. Redman argues that while these scoring systems may have helped to standardise opinions, they are unable to offer the levels of consistency and accuracy provided by computerised analysis. “If you take a single trace and show it to a variety of individuals they will differ widely in opinion on its clinical significance. If you show it to a group of experts, this variation may be less apparent, but it is unlikely that the person at the bedside will be a top expert. If you show a trace to the same person on two occasions, six months apart, they will often contradict themselves and express a different interpretation from their original opinion. With a computerised system, you will arrive at the same conclusion every time.”

Dawes Redman system