Maternal Heart Rate in Labor and the Potential for Confusion With Fetal Heart Rate [20L]

Abstract

INTRODUCTION: A source of error in electronic fetal monitoring occurs where there is confusion between the maternal heart rate (MHR) and the fetal heart rate (FHR). The fetal transducer can detect the MHR rather than the FHR. We studied the MHR during labor to determine the proportion of cases where the MHR was in the fetal range (>110 bpm) and could potentially cause confusion. METHODS: Consecutive cases of low risk patients in labor were studied. Cases required a minimum of 2 hours of archived continuous electronic monitoring of both the MHR (by oxygenation saturation probe) and FHR prior to full dilatation. For individual patients, MHR baseline was averaged over each hour in labor and the results express as the proportion of all MHRs >110 bpm during each hour before and after full dilatation. RESULTS: There were 80 labors included in the study with data available for a total range of 10 hours. In the first stage only 2.5% of labors had an MHR>110 bpm 7 hours prior to full dilation, rising to 15% at full dilatation. In the second stage this rose to 30% after 2 hours and 45% after 3 hours. CONCLUSION: An MHR in the fetal range is common in labor especially in the second stage. The potential for confusion is very significant and this can lead to poor outcomes if an abnormal FHR is misidentified as MHR in the apparently normal range.

Approaches to Preventing Intrapartum Fetal Injury

“…Occasionally, the CTG system inadvertently records the maternal heart rate (MHR) rather than that of the fetus (120,121). The MHR may appear very similar to the FHR pattern, especially with maternal tachycardia.…”