A checklist was suggested to be used at the start of recording (Table 1). STAN calculates the initial reference baseline T/QRS using the first 20 T/QRS data recorded and resets the baseline if it becomes lower or after 3 hours of recording. A ST rise is detected when a sequence of T/QRS data are recorded, which significantly exceeds this T/QRS baseline, and an ST event is flagged by the computer. In a case of pre-existing fetal hypoxia, the ST change may have already taken place and further ST rise may not occur. Therefore, STAN recordings should start during the first stage of labour, with ideally a reassuring FHR trace.

Based on a large prospective study where acid?base values were evaluated with CTG and ECG changes, the expert group considers it acceptable to start STAN monitoring on a nonreassuring CTG trace if the previous FHR pattern includes signs of reactivity (accelerations and/or FHR variability).² Abnormal FHR at the start of recording without previous FHR information requires assessment of the fetal state prior to the application of STAN, for example analysis of fetal scalp pH and/or FHR reactivity with digital or vibroacoustic stimulation. Absence of ST events in a situation with nonreassuring FHR trace from the start could be related to previous compromise in a fetus that is unable to respond with ECG changes. If additional assessment of the fetal condition in such a case is not possible, the need for intervention should be based on FHR, clinical situation and fetal blood sampling (FBS) but not on STAN information.

Fetal ECG ST analysis requires good signal quality. Continuous data (with at least one T/QRS ratio/minute) are needed to obtain reliable ST information. Gaps in the T/QRS ratios for more than 4 minutes may result in missed STAN events. This is particularly important in the presence of intermediary or abnormal FHR and during second stage when the condition of the fetus may deteriorate rapidly.

The reference T/QRS baseline calculated previously is kept when the machine is temporarily disconnected by using the ?temporary end? function. However, ST events that may occur during the disconnected period will not be detected. Therefore, pausing a recording when the FHR is abnormal is not recommended, as significant STAN events may be missed. If the FHR has become abnormal during temporary disconnection, the situation maybe similar to starting a recording with an abnormal trace, that is there is a need to check the fetal status using FBS or stimulation tests.

With the use of STAN, the FHR pattern is classified according to the International Federation of Obstetrics and Gynecology guidelines.³ With a combination of several intermediary observations, the FHR should be classified as abnormal (Table 2). Calling for additional expertise in assessing FHR should be considered an intervention and is as important as alleviation of the cause(s) of fetal compromise, such as stopping oxytocin infusion or repositioning of the mother.

In rare cases, the FHR pattern may gradually change from normal to abnormal, without the appearance of ST events (see paper by Westerhuis et al.in this issue).¹ An abnormal FHR pattern for more than 60 minutes (or earlier if the CTG deteriorates rapidly) with normal ST requires qualified assessment and checking for nondeteriorating fetal state (with a preterminal FHR pattern, intervention is always indicated, irrespective of the ST data.

Intervention depends on the cause of fetal compromise and the stage of labour. During the first stage, interventions may consist of intrauterine resuscitation (cessation of oxytocin infusion and/or acute tocolysis in cases of excessive uterine contractions), correction of maternal hypotension or amnioinfusion. A caesarean section is only one of the options. Recovery requires both CTG and ST to be normalised and a FBS may be required to verify recovery. During the second stage of labour with active pushing, immediate operative delivery is recommended, unless spontaneous delivery is to be anticipated in the next 5?10 minutes.

In the presence of STAN event and suspicious or abnormal CTG calling for intervention according to the STAN guidelines, this should be undertaken within 20 minutes (Table 3).

STAN is a method for detection of acute intrapartum asphyxia not fetal infections. In the presence of maternal pyrexia, even intermediary FHR changes may be regarded as significant in connection with an ST event.

Biphasic (BP) ST events should be considered in relation to the window of recording. This implies that two BP events in combination with an abnormal CTG calls for intervention. The time-span between the BP should be related to the clinical situation. Appropriate and consistent classification of the FHR patterns is still the weakest link in intrapartum monitoring, as education and training in FHR interpretation is not as widespread as the method itself.

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