Summary of main results
The main reason for the introduction of continuous intrapartum cardiotocography (CTG) monitoring in clinical practice was a belief that it would reduce rare but devastating outcomes - perinatal death and neonatal hypoxic brain injury in otherwise healthy babies. However, this review found no statistically significant difference in perinatal deaths between pregnancies monitored during labour with continuous CTG compared to those monitored those intermittent auscultation. The overall quality of evidence that underpins this conclusion has been judged as 'moderate' (Summary of findings table 1). It does, however, seem unrealistic to expect that any intrapartum intervention in modern maternity care will result in a statistically significant improvement in perinatal deaths. In order for a trial to test a realistic hypothesis that continuous CTG can prevent one death in one thousand births (0.1%), more than 50,000 women would have to be randomised. It is, therefore, more logical to concentrate on short- and long-term childhood morbidity. Unfortunately, very few clinically relevant neonatal outcomes have been reported consistently in all trials.
For decades, low Apgar scores have been used as a surrogate measure for birth asphyxia and subsequent adverse neurodevelopmental outcomes. Recent evidence has confirmed a strong association between low Apgar score and cerebral palsy in both low and normal birthweight infants (Lie 2010). This review found no evidence that use of continuous intrapartum CTG monitoring has an impact on Apgar score. However, there were very few babies with clinically significant low Apgar scores in studies that assessed this outcome. Therefore, potentially important differences between the two groups cannot be ruled out.
Hypoxic ischaemic encephalopathy, a more robust measure of hypoxic brain injury, was only reported in one study (Athens 1993). In the absence of any meaningful long-term follow-up data, the impact of continuous CTG monitoring on a neonate can only be evaluated based on the data from two clinically important outcomes, i.e. neonatal seizures and cerebral palsy.
For both neonatal seizures and cerebral palsy, the majority of data are provided by Dublin 1985. At first glance, the data appear contradictory. There is a significant reduction in neonatal seizures in the continuous CTG group, but no impact on cerebral palsy. If anything, the rates of cerebral palsy appear to be higher in the continuous CTG group, although the pooled result did not reach statistical significance. This apparent increase in cerebral palsy in children monitored by CTG comes from Seattle 1987. However, the results from this study, the only study of CTG monitoring during preterm labour, are not statistically significant using 99% confidence intervals. In addition, this study excluded infants with a birthweight of more than 1750 grams (34% of randomised cohort) which may be a source of bias. Given that all other outcomes in this trial, including caesarean section rates, neonatal seizures and deaths were almost identical this may have been a chance finding and should be interpreted with caution.
It is now generally accepted that cerebral palsy is more often caused by antepartum, rather than intrapartum, events (Palmer 1995). It may, therefore, be unrealistic to expect that intrapartum interventions will have the capacity to achieve a significant reduction in cerebral palsy. There are, clearly, some cases of cerebral palsy that are a direct consequence of intrapartum hypoxic injury. These cases are very rare, and even systematic reviews of randomised trials are unlikely to have sufficient power to test intrapartum CTG as a method to reduce cerebral palsy caused by acute and avoidable intrapartum events.
The reduction in seizures associated with continuous CTG monitoring is important, but has to be interpreted cautiously in the absence of good quality long-term follow-up data. It has been suggested that seizures may be a "sentinel event" of a peripartum adversity that does not necessarily always manifest itself as hypoxic encephalopathy (Dennis 1978; Derham 1985, Keegan 1985; Lien 1995; Spellacy 1985). When asphyxia, infection, brain malformations and metabolic causes are excluded, some neonatal seizures are associated with cerebral infarction or neonatal stroke (Estan 1997; Lien 1995). Although the underlying causes are not well understood, neonatal seizures may have long-term consequences other than cerebral palsy. One longitudinal study found that some babies who had neonatal seizures were classified as normal at five years and had normal overall intelligence in adolescence as assessed by IQ tests, but had some abnormal results on detailed neuropsychological testing (Temple 1995). Clearly, there is a need for comprehensive long-term follow-up of the randomised cohorts that is not limited to extreme adverse outcomes such as cerebral palsy, but also includes more subtle neuropsychological assessment.
The results of this review demonstrate that continuous CTG monitoring leads to an increase in caesarean sections. Such an effect of continuous CTG is clinically plausible as CTG monitoring leads to more interventions (e.g. fetal blood sampling, amniotomy) and more diagnoses of presumed fetal compromise for which emergency caesarean section is seen as the only safe management option. However, the overall quality of evidence for this outcome was judged as 'low' (Summary of findings table 1) and, therefore, the observed increase has to be interpreted cautiously. It is noteworthy that size and direction of the effect on caesarean section was consistent for pre-specified subgroups, including high quality trials and trials where clinicians had access to intrapartum fetal blood sampling. Subgroup interaction test was only significant (I2 = 81.6%) for studies in low-risk, high-risk and mixed-risk status, but the heterogeneity comes from a mixed group. The impact of CTG monitoring on caesarean section in low-risk and high-risk populations appears to be virtually identical, which is contrary to recommendations from many professional bodies providing guidance on intrapartum fetal monitoring.
There was some evidence that labour was more painful in the continuous CTG group, but the statistically significant increase in the 'need for any analgesia' included general anaesthesia. It is, therefore, likely that this difference was caused by an increase in the number of caesarean sections, rather than necessarily more painful labour. Women do report more pain when lying on their backs during labour. At the times when the studies in this review were undertaken (between 1976 and 1994), women in the intermittent auscultation group may well also have been on their backs and not using mobility and positions to help them with their labours. There were no data from the trials included in the review to allow any analysis of this potential confounder.
We have prespecified several subgroups that could have been expected to influence the direction and size of the differences compared with results when all trials are considered together. We were conscious that any differences between subgroups and overall results would have to be interpreted with extreme caution (Rothwell 2005). With this proviso, we found no subgroup differences of clinical importance, but the number of trials and women in subgroups was relatively small.
Overall completeness and applicability of evidence
Clearly, the lack of long-term follow-up data and inadequate reporting of the data according to the clinically important subgroups is regrettable and limits the applicability of the evidence.
Quality of the evidence
The overall quality of the evidence can be best described as low to moderate and has been summarised in the Summary of findings table 1.
Potential biases in the review process
Our selection of outcomes in general and primary outcomes in particular might have been influenced by our knowledge of the published literature and the first Cochrane review on this topic (Thacker 2001).
Agreements and disagreements with other studies or reviews
Some large cohort studies suggest much more profound benefit on neonatal morbidity and mortality (Chen 2011). Some observational data also suggest the benefit of fetal blood sampling during labour in cases of suboptimal CTG, (Stein 2006) but we found no evidence that the increase in caesarean section rate was greater if fetal blood sampling was unavailable; nor did access to fetal blood sampling influence the difference in neonatal seizures or any other prespecified outcome.