Interpretation of the fetal ECG during labor: the effect of uterine contractions

The effect of uterine contractions on the T/QRS ratio of the fetal electrocardiogram

“…The increase in T/QRS ratio during contractions found in this study (1.02%) is less than the 8% reported by THALER et al [9], the reasons for this are not clear. The data processing system used by THALER et al [10] was broadly similar to our own with specific steps taken to avoid the T wave attenuation caused by beat-to-beat variations in the RT interval.…”

“…This and other subtle differences in the steps taken to overcome the effect of noise could also account for the differences between our studies. For example in some ECG records we noted more baseline wander during uterine contractions which, if not excluded, might account for the increase in the T/QRS ratio found by THALER et al [9] during contractions. It was also reported by TteALER et al [10] that the increase in T/QRS ratio occurred predominantly in the first half of the contraction.…”

“…The data processing system used by THALER et al [10] was broadly similar to our own with specific steps taken to avoid the T wave attenuation caused by beat-to-beat variations in the RT interval. THALER et al [9] analysed only five consecutive contractions per subject but gave no reason for this nor about the manner in which the contractions were selected. This and other subtle differences in the steps taken to overcome the effect of noise could also account for the differences between our studies.…”

“…Earlier studies have noted that short term changes in the height of the T wave can occur during or shortly after contrarctions [1,4]. One study of 25 low risk women found an 8% increase in the T/QRS ratio during contractions [9]. It was argued that this represented a response to an increase in circulating catecholamines during contractions.…”

“…It was argued that this represented a response to an increase in circulating catecholamines during contractions. If the fetal ECG is to play an important part in the assessment of intrapartum welfare, it is important that the brief, but apparently abnormal, changes described by T ALER et al [9] are investigated further. In a previous study [6] we were able to examine the effect of contractions on the T/QRS ratio in eight normal subjects but our findings were not consistent.…”