ST analysis

A message from the heart

ST analysis is made up of a number of parameters that work in unison to continually analyze and detect changes in the fetal ECG waveform.

ST analysis automatically detects and alerts changes that are related to the risk of fetal hypoxia. ST analysis always works in parallell with the information from the fetal heart rate, adding valuable information about the fetal state to the CTG tracing.

Changes in the ST interval of the fetal ECG helps the clinician to detect signs of hypoxia and shows how the fetus handles the stress of labour.

The fetal ECG contains a lot of useful information, but it is only in recent years that we have been able to use this knowledge and information to its fullest extent. Thanks to technical development, the signal processing technology is now able to accurately record the fetal ECG waveform. The condition of the fetal heart reflects the condition of the brain, and the ST waveform reflects the energy balance in the myocardium.
A normal ST waveform demonstrates a sufficient fetal oxygen supply. During hypoxia the T-wave amplitude of the ECG increases and the STAN monitor displays an automatic ‘ST event’ alert. The Stan method is a combination of standard CTG parameters and ST analysis. If there is a significant change in the ST interval and a ‘ST event’ alert is displayed, actions are recommended according to clinical guidelines

Despite developments in labor management, the need remains to decrease fetal injury and mortality rates. Standard CTG has a high specificity for classification of normality and severe pathological traces. ST analysis grades the deviation.

The combination of ST analysis and standard CTG parameters provides extended and more accurate information about the fetus during labor than CTG alone.

ST analysis is automatic and continuous, with proven effectiveness in large randomized, controlled trials. By providing clinicians with more precise information about the fetal state during labor, fetuses at true risk can be detected, and unnecessary interventions are avoided.

The Stan method is a cost effective alternative to CTG alone. In a recent health economic study, a decision-tree model was used to compare the two treatment strategies. Baseline estimates were derived from the literature, while costs and effects were extrapolated to a lifetime perspective. Also taken into account was the probability of developing cerebral palsy and its effect on quality adjusted life years. The analysis showed that the Stan method was both more effective and less costly than using CTG alone. Significant quality adjusted life years (QALY) were gained by using the Stan method.

ST analysis has been evaluated in a large number of studies. The basic research was initially performed in preclinical animal studies in the early 1970s. The first clinical randomized controlled trial 4 was published in 1993. The Cochrane Review on fetal ECG during labor supports the use of ST Analysis.

  • The Cochrane Review on fetal ECG

    The Cochrane Review on fetal ECG The objective of this review was to compare the effects of analysis of fetal ECG waveforms during labor with alternative methods of fetal monitoring. Three trials based on ST analysis were included in the meta-analysis, which showed that ST waveform analysis was associated with fewer babies suffering severe metabolic acidosis at birth. This was achieved along with fewer fetal scalp samples and fewer operative deliveries. The review concludes that the findings provide support for the use of fetal ST analysis when a decision has been made to perform continuous electronic fetal heart rate monitoring during labor.

  • The Swedish Randomized Controlled trial

    The Swedish Randomized Controlled trial This was the second, large-scale Randomized Controlled trial to compare outcome after using CTG alone and CTG in cobination with ST analysis. The study included 4 966 term fetuses in three large labor wards in Sweden. After exclusion of inadequate recordings and fetuses with malformations (574 fetuses in all) the findings showed a 61 % decrease in the number of fetuses born with cord artery metabolic acidosis in the CTG+ST group, at the same time as a 28 % decrease in operative interventions due to fetal distress. These findings were in line with the results from the Plymouth trial: it was concluded that intrapartum monitoring with CTG combined with automatic ST analysis, increases the ability of the obstetrician to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.

  • Follow-up of the children from the Swedish trial

    Follow-up of the children from the Swedish trial. The aim of the study was to evaluate the neonatal outcome of the Swedish Randomized Controlled trial, focusing on complicated or adverse neonatal cases. The results show a reduction in the incidence of newborn infants with marked neurological symptoms in the CTG+ST group. Of the 29 fetuses from both arms with complicated or adverse outcome, 22 fetuses had presented a fetal heart rate and ST pattern that indicated a need for intervention according to the Stan clinical guidelines. There was a significant decrease in the number of live-born with moderate or severe neonatal encephalopathy in the CTG+ST group, compared to the group of CTG alone. The authors concluded that the most important finding of the study was the prevalence of ST changes that are detected at an appropriate point in time to allow for earlier and more consistent intervention.

  • STAN US clinical usage study

    STAN US clinical usage study. This is a prospective, non-randomized study enrolling 530 patients from diverse populations and providers in six university and community medical centres. It is the first clinical usage study of ST analysis in the US. The objective of the study was to show that US obstetrical staff, once trained, can appropriately interpret and apply the Stan method. The study included a structured training program and a pilot and credentialing phase before the actual clinical use. The results of the study demonstrated that ST analysis can be applied to support obstetric decision making and that unnecessary interventions for non reassuring fetal heart rate can be safely avoided. The authors conclude that US clinicians can use the ST analysis effectively and in a manner similar to that of experienced Stan users.

  • Virtual study reviewing Stan tracings

     Virtual study reviewing Stan tracings. The aim of this study was to evaluate if the addition of ST analysis to standard CTG would improve the consistency and accuracy of clinical decision-making for intervention during labor. Seven experienced European Stan users performed a blinded CTG interpretation on the same 51 completed intrapartum cases containing examples of both healthy and compromised term fetuses. When ST analysis was added to the CTG, the rate of intervention was significantly decreased for cases with pH >7.14. More importantly, the observer agreement demonstrated a marked improvement in the timing of appropriate intervention, from 68 % to 92 % with the addition of ST analysis.

  • Stan in clinical practice

    Stan in clinical practice. This is a prospective observational study of the introduction of ST analysis in two maternity wards during two years in the city of Goteborg, Sweden. Out of the total population of 14 687 term deliveries, 4 830 were monitored using ST analysis. The units were equipped with eight Stan units and an additional three units the last six months of the study. The usage of ST analysis increased from 28.1 % the first year to 37.7 % the second year and was associated with a significant reduction in metabolic acidosis in the total population from 0.76 % to 0.44 % respectively. The rate of operative deliveries in the total population did not change during the study period.

  • Fetal ECG and Stan technology – a review

    Fetal ECG and Stan technology – a review. This review of the Stan method includes physiological, signal processing and clinical aspects. The two randomized controlled trials comparing ST analysis and CTG combined, to CTG alone, have shown a significant decrease in children born with metabolic acidosis along with a decrease in operative deliveries due to fetal distress. In addition, inter-observer agreement for ST analysis was higher than for CTG alone. The review highlights the importance of educational models, as described in several studies. The authors conclude that ST analysis and CTG combination, have the potential to significantly improve outcome when appropriate education, training and use of Stan according to guidelines are provided. Please see publications here.


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