CTG or STAN – with or without FBS?


Fetal monitoring is a fundamentally important but still controversial topic in obstetrics. In obstetrics there is a kind of “tradition” of introducing methods of surveillance or intervention before we have proper evidence for the proposed benefit. Fetal blood sampling (FBS) and ST-analysis + cardiotocography (CTG) (STAN) is no exception. Actually, we never even had evidence, at least not from randomized controlled trials (RCTs), that CTG was better than intermittent auscultation in terms of fetal outcome before it was widely distributed and ingrained in clinical practice in high- and even medium-resource countries. We do know that in controlled prospective trials the rates of cesarean section and operational delivery increased after introduction of electronic CTG, but this does not seem to have improved fetal/neonatal or long-term outcome to any significant degree [1]. We have several different consensus algorithms for the interpretation of CTGs, and we use most of our time in the obstetric unit to discuss and interpret CTG traces.

Therefore, the promising results of the first RCT studies of STAN raised enthusiasm among obstetricians. But subsequent trials and meta-analyses showed divergent results. In the autumn 2013, a courageous colleague in Malmö invited international speakers to a Pro and Con conference on FBS and STAN, and we decided to invite these speakers to write commentaries for this theme issue.

The STAN method has been evaluated by five different RCTs, and five systematic reviews with meta-analyses have been published – with different results. To present the background material we have agreed to publish reviews describing both the RCTs and the meta-analyses. Since there is a subjective approach involved regardless of who is the author, we have invited a leading academic from each of the Nordic countries where the STAN has been in use to comment on the presentation of the RCTs and meta-analyses. These comments appear after the relevant two articles.

The aim of this theme issue is not to provide clear-cut recommendations or definite answers as to whether to apply FBS and or STAN in clinical practice as adjuncts to conventional CTG monitoring. We wanted to present the pros and cons for both fetal monitoring methods. We are aware that the intense debate that followed the publication of the dominant Swedish study was sensitive and even emotional, especially considering our usually cool Nordic temper.

But still, the way we apply fetal monitoring in labor and interpret the CTG traces is an essential part of our daily work with midwives in the delivery ward. It is important for all of us. Some find it counterproductive that FBS is even used to confirm or supplement the results obtainable by STAN. Others do not believe in STAN and advocate continued use of CTG and FBS for measuring pH, base excess and/or lactate levels.

The development of STAN was based on many years of published experimental research. We know less about the background for decisions on the renewed specific interpretation of the CTG that was instituted by implementing STAN monitoring. We do not know enough about how the STAN concept was developed. What was the background material that led to the definition of “significant” STAN events and how significant were they in the material of deliveries used for development of the concept? How did the researchers decide on a baseline rise of 0.06 as significant – why not 0.05 or 0.08? To some obstetricians, STAN is only a vehicle towards understanding a CTG that puzzles you and makes you scrutinize the pattern. But the absence of a clear background and the lack of transparency convey a sense of a Magic Black Box. In general terms the algorithm tells you that an ST event loses its significance if the CTG is normal – thus the CTG “overrules” the ST analysis unless you have a pathological CTG trace with no ST events. The exception is when the trace is very pathological (pre-terminal), as the ST registration is then considered useless. The non-intuitive method occupies a lot of intellectual capacity, and the clinical focus on the screen and the complex algorithm gets priority before the proactive support for the mother and before the required focus on the progress of labor, which so often is different from the linear average depicted in a partogram.

The FBS conveys a sense of knowing the true state of the fetus. The human inclination to perceive linear relations and development, extrapolating from the average to the individual level, may mislead us when we perform a cesarean section because of a scalp pH of 7.19 at 8 cm cervical dilation, and without cancellation of an oxytocin drip that caused uterine hypertonia and which might have normalized the pH. Base excess and lactate could provide additional information on accumulating acidosis and be more useful, but prospective studies are still needed to help us out on that.

Fetal monitoring is an important part of delivery care, especially in settings with high rates of induction where prolonged labor may ensue and where active management with a risk of hyperstimulation is practiced. Progression of labor is an integrated factor in clinical decision-making when abnormal CTG patterns occur. A recent USA consensus document presents an algorithm for obstetric interventions taking into account different characteristics of intermediate, suspicious CTGs (type II) [2]. The consensus algorithm has been discussed and questioned, disclosing the lack of a scientific background [3, 4]. The algorithm includes progression as well as the actual stage of labor. Although the algorithm is complex, it does not include STAN, which would have made interpretation even more difficult and would have necessitated computerized assistance.

Most obstetricians with several years of experience feel that we should be able to integrate more than two or three dimensions of fetal monitoring for increased reliability when we decide on clinical management. We should also balance mechanical and physiological signs and events in labor and integrate the progress of delivery into the decision-making. There is no way back to a general policy of intermittent auscultation. Auscultation causes even more uncertainty. When more knowledge on the condition of the fetus s needed, we require interpretation of the fetal heart rate pattern and we need to decide on the possibility of impending acidosis as well as documentation for litigation purposes.

The use of STAN and FBS differs between obstetric units in the Nordic countries. Of course the unit was never randomized, but it might be possible to perform a simple comparison of maternal and fetal/neonatal outcomes using the Nordic Medical Birth Registries. We would also be able to identify centers of excellence with the best maternal and neonatal outcomes in comparable populations – and ask for their policies and routines of fetal monitoring – items that are not included in the birth registry information.

Fetal monitoring during labor is an important issue. On balance, fetal surveillance during labor does probably more good than harm. We do use a lot of resources on it, which it is difficult to get away from. The focus is on fetal heart rate patterns and on the question of fetal acidosis. Documentation for audit and medico-legal purposes is another issue that is not part of individual patient care, but matters in a wider sense. The vast resources spent on fetal monitoring should result in improved health outcomes for the mother and her neonate. We need better methods for fetal monitoring developed in collaboration between obstetricians, physiologists and perinatal epidemiologists. Both for the sake of the mother and her child we need proof of the efficacy of the methods used!