Changes in the ST‐interval segment of the fetal electrocardiogram in relation to acid–base status at birth

Abstract

Objective To assess the occurrence of ST-interval segment changes of the fetal electrocardiogram (ECG) and cardiotocographic (CTG) abnormalities preceding acidaemia at birth.Design Case-control study.Setting University hospital labour ward.Sample Newborns with severe cord artery metabolic acidaemia (pH < 7.00 and lactate ‡ 10 mmol/l; n = 24), moderate metabolic acidaemia (pH 7.00-7.09 and lactate ‡ 10; n = 48), acidaemia (pH 7.00-7.09; n = 52), pre-acidaemia (pH 7.10-7.19; n = 265), and controls (pH ‡ 7.20; n = 117).Methods Monitoring traces were assessed blinded to outcome.Main outcome measures CTG and ST changes.Results Any ST event occurred significantly more often among cases with severe (79%) and moderate (75%) metabolic acidaemia than among controls (50%). The difference was restricted to baseline T/QRS rises and to the second stage of labour, during which any event only occurred significantly more often among cases with severe metabolic acidaemia (62%) than among controls (38%). ST events coincided with abnormal CTG patterns in 67, 44, 40, and 28% of cases with severe and moderate metabolic acidaemia, acidaemia, and pre-acidaemia, respectively, and in 12% of controls. ST events with intermediary CTG were similarly frequent in the case groups (0-6%) as in the controls (4%). The ST guidelines stated intervention in 96, 62, 73, and 49% of case groups and 23% of controls.Conclusions Only two of three cases with severe and less than half of cases with moderate metabolic acidaemia were preceded by ST events coinciding with CTG abnormalities. It is therefore important to intervene for long-lasting, rapidly deteriorating or marked (preterminal) CTG abnormalities, also in the absence of ST events.

FIGO consensus guidelines on intrapartum fetal monitoring: Adjunctive technologies

“…A CTG with normal variability and accelerations or a normal FBS is required at the start of monitoring for a confident evaluation of ST data, but even then hypoxia/acidosis can rarely develop during labor without the occurrence of ST events. Finally, ST events have been reported in about 50% of normally oxygenated fetuses, but only in 16% were they associated with abnormal CTG patterns warranting intervention according to the STAN guidelines [58].…”

Fetal monitoring with computerized ST analysis during labor: a systematic review and meta‐analysis

“…In the RCTs (33–37) and in the observational study by Norén et al (38), umbilical artery metabolic acidosis was defined as pH <7.05 and BE < −12 mmol/L. In the case–control study (39) lactate >10 mmol/L was used as a criterion instead of BE. A pH difference of at least 0.03 between artery and vein was used by Westerhuis et al (34,35) to ensure that one of the two samples was from the artery.…”

“…The case–control study (39) reported intervention rates in relation to different grades of fetal metabolic acidemia at birth. Intervention was recommended in 96% of the cases with severe metabolic acidemia and in 62% of the cases with moderate metabolic acidemia according to STAN® clinical guidelines, whereas the corresponding figures for CTG only were 92 and 46%.…”

ST waveform analysis for monitoring hypoxic distress in fetal sheep after prolonged umbilical cord occlusion

“…In a previous paper we calculated waveform-based ECG markers, during normoxemia and hypoxemia. Also, the absence of STAN-events due to poor signal quality in human fetuses associated with metabolic acidosis has been reported in literature [ 25 , 26 ]. We conclude that improvement of the algorithm might result in more sensitive event warning.…”