Jenny A. Westgate

A multicentre comparative study of 17 experts and an intelligent computer system for managing labour using the cardiotocogram

Objectives To investigate 1. whether an intelligent computer system could obtain a performance in labour management comparable with experts when using cardiotocograms (CTGs), patient information, and fetal blood sampling and 2. whether experts could be consistent and agree in their management of labour.

Antecedents of neonatal encephalopathy with fetal acidaemia at term

Objective To identify the relative contribution of antenatal hypoxia, obstetric catastrophe during labour and fetal monitoring practice to the occurrence of neonatal encephalopathy associated with acidaemia at term.

Fetal heart rate variability changes during brief repeated umbilical cord occlusion in near term fetal sheep

Objective To determine whether changes in fetal heart rate variation during repeated umbilical cord occlusions reflect evolving cardiovascular compromise in near term fetal sheep.

The myths and physiology surrounding intrapartum decelerations: the critical role of the peripheral chemoreflex.

A distinctive pattern of recurrent rapid falls in fetal heart rate, called decelerations, are commonly associated with uterine contractions during labour. These brief decelerations are mediated by vagal activation. The reflex triggering this vagal response has been variably attributed to a mechanoreceptor response to fetal head compression, to baroreflex activation following increased blood pressure during umbilical cord compression, and/or a Bezold–Jarisch reflex response to reduced venous return from the placenta. Although these complex explanations are still widespread today, there is no consistent evidence that they are common during labour. Instead, the only mechanism that has been systematically investigated, proven to be reliably active during labour and, crucially, capable of producing rapid decelerations is the peripheral chemoreflex. The peripheral chemoreflex is triggered by transient periods of asphyxia that are a normal phenomenon associated with all uterine contractions. This should not cause concern as the healthy fetus has a remarkable ability to adapt to these repeated but short periods of asphyxia. This means that the healthy fetus is typically not at risk of hypotension and injury during uncomplicated labour even during repeated brief decelerations. The physiologically incorrect theories surrounding decelerations that ignore the natural occurrence of repeated asphyxia probably gained widespread support to help explain why many babies are born healthy despite repeated decelerations during labour. We propose that a unified and physiological understanding of intrapartum decelerations that accepts the true nature of labour is critical to improve interpretation of intrapartum fetal heart rate patterns.

Antenatal antecedents of moderate or severe neonatal encephalopathy in term infants – a regional review

Background: Regional audits of term infants with neonatal encephalopathy (NE) provide an opportunity to examine issues related to causation and quality of care.

Fetal heart rate overshoot during repeated umbilical cord occlusion in sheep

Objective To assess the clinical utility of overshoot fetal heart rate (FHR) decelerations by examining their occurrence after umbilical cord occlusions of varying frequency and length in near-term fetal sheep. Methods Fetuses were allocated to the following three groups: 1-minute umbilical cord occlusion repeated every 5 minutes (1:5 group, n = 8) or every 2.5 minutes (1:2.5 group, n = 8) or 2-minute occlusions repeated every 5 minutes (2:5 group, n = 4). Occlusions were continued for 4 hours or until fetal mean arterial pressure decreased below 20 mmHg during two successive occlusions. Results In the 1:5 group, fetuses tolerated 4 hours of occlusion without hypotension or clinically significant acidosis and overshoot never occurred. In the 2:5 group, fetuses rapidly became hypotensive and acidotic, and occlusions were terminated at 116.3 ± 22.9 min (mean ± standard deviation). Overshoot was seen after every occlusion, starting with the first occlusion. In the 1:2.5 group, fetuses became progressively acidotic and hypotensive and occlusions were stopped at 183.1 ± 42.8 min. Overshoot occurred after 91.6 ± 42.5 minutes, at a pH of 7.17 ± 0.06, base deficit 9.3 ± 4.5 mmol/L. After the appearance of overshoot there was a more rapid decrease in fetal mean arterial pressure (0.25 [0.21, 0.35, 25–75th percentile] mmHg/minute versus 0.11 [0.03, 0.15] mmHg/minute before overshoot appeared, P < .01). Conclusion These data suggest that overshoot is related to longer (2-minute) occlusions or to developing fetal acidosis and hypotension during 1-minute occlusions. This pattern could have clinical utility, as 1-minute contractions are typical of active labor.

Do fetal electrocardiogram PR-RR changes reflect progressive asphyxia after repeated umbilical cord occlusion in fetal sheep?

The aim of this study was to determine whether there is a relationship between changes in PR-RR correlation of the fetal ECG and progressive changes in fetal acid-base status and blood pressure (BP) during repeated umbilical occlusion. Chronically instrumented fetal sheep at 126.8 ± 0.6 d (mean± SEM) were randomized to receive 1 min of total umbilical cord occlusion either every 5 min for 4 h (1:5 group; n = 8), or every 2.5 min until BP fell <2.7 kPa (20 mm Hg) on two successive occlusions (1:2.5 group; n = 8). The PR-RR correlation was determined in 5- or 2.5-min intervals. Umbilical cord occlusion caused variable decelerations with initial sustained hypertension. In the 1:5 group BP remained elevated throughout, and there was little change in acid-base status (pH = 7.34 ± 0.07, base deficit = 1.3 ± 3.9 after 4 h). In contrast, after the third occlusion the 1:2.5 group showed progressive hypotension during occlusions, and severe progressive metabolic acidemia (pH 6.92 ± 0.1, base deficit 17.0 ± 4.7 mmol/L after the last occlusion). In both groups, the PR-RR relationship switched from positive to negative with the onset of occlusions, then reverted to positive after a variable interval. In the 1:2.5 group later reversion of the PR-RR to positive was associated with earlier and more prolonged hypotension during the middle and end of the occlusion series (p < 0.001). We conclude that the initial switch to a negative PR-RR relationship during repetitive umbilical occlusion was due to a reflex-mediated response unrelated to fetal acidosis or hypotension. Both stable well compensated fetuses and severely hypoxic, hypotensive fetuses subsequently showed a positive PR-RR correlation.

Meconium and fetal hypoxia: some experimental observations and clinical relevance

In an experimental study, chemically sympathectomised near term fetal sheep and a control group were subjected to repeated episodes of acute hypoxia. Despite severe hypotension and metabolic acidosis, no animal in the control group had meconium‐stained amniotic fluid, whereas every animal in the sympathectomised group had heavily meconium‐stained amniotic fluid at the end of the experiments. These data and the available literature do not support a direct association between acute hypoxia and meconium‐stained amniotic fluid but suggest that a reduction in sympathetic neural tone must be a component of meconium passage. Clinical and experimental data on the occurrence of meconium‐stained amniotic fluid are reviewed.

Suitability of fetal scalp electrodes for monitoring the fetal electrocardiogram during labour

As the limitations of heart-rate based intrapartum monitoring have become apparent, there is renewed interest in analysis of the fetal electrocardiographic waveform as obtained from a fetal scalp electrode. A high quality ECG signal is necessary for waveform analysis. This study examined the suitability of five commonly available scalp electrodes for collecting this signal by examining their physical and electrical characteristics, together with a randomised clinical trial in which the ECG trace quality was assessed in 50 patients. The frequency response of Copeland electrodes was such that they attenuate the ECG signal more than the baseline noise. Difficulties were experienced in obtaining optimum attachment and the long, semi-rigid design increased movement artefact resulting in significantly poorer quality ECG signals. Whilst the Hewlett-Packard double spiral electrode had a near ideal frequency response, certain design features made it difficult to apply and remain secure so the clinical signals were of intermediate quality. The Corometrics and Cetro single spirals had the most stable attachment to the scalp and a near ideal frequency response, so produced significantly better signal quality in the clinical trial. Currently, single spiral electrodes are the most suitable for electrocardiographic data collection.

Fetal seizures causing increased heart rate variability during terminal fetal hypoxia

Fetal seizures together with both abnormal breathing movements and fluctuations in fetal blood pressure and heart rate resulting in increased fetal heart rate variability have been observed in brain-damaged fetal sheep shortly after an asphyxial insult. We report a clinical example of convulsions and increased heart rate variability during terminal fetal hypoxia.