Fetal Monitoring and the Challenges of Identifying the Fetus at Risk of Intrapartum Hypoxia

The relationship between maternal anemia and electronic fetal monitoring patterns

Intrapartum fetal surveillance

Intrapartum fetal surveillance is still under debate, despite 30 years of clinical experience and numerous clinical trials. Waveform analysis of the fetal electrocardiogram has emerged not as an alternative to cardiotochography but as a support tool to allow more accurate interpretation of intrapartum events. During hypoxia, the healthy fetus is utilizing a series of defense mechanisms. Among these, the increase in sympathetic activity, with an increase in circulating adrenaline, activates the myocardium with an increase in workload (the product of cardiac output, myocardium contractility and blood pressure). If there is an imbalance between myocardial oxygen supply and consumption, determined by the workload, then anaerobic metabolism, with a breakdown of myocardial glycogen stores starts and high T waves emerges. ST depression with negative T waves has recently been observed during hypoxia experiments in experimentally growth retarded guinea pigs whilst their normally grown littermates showed ST elevation. These findings have stimulated the development of a dedicated fetal ECG monitor - STAN - incorporating both standard CTG and ST waveform analysis. The STAN concept has now been taken through the process of recognized validation including several prospective studies and a large randomized trial in Plymouth of 2400 high risk, term deliveries. The T/QRS ratio is only one parameter to be used - equally important is to identify the occurrence of ST depression with biphasic negative T waves and to interrelate the CTG and the ST waveform as outlined in the clinical guidelines (table I). This table contains the clinical experience gained over many years and has formed the basis for the first randomized controlled trial comparing ST waveform + CTG with CTG only. Obviously, when the T/QRS ratio is used as the only component of such a scheme, confusion emerges. The analysis should also contain cases with significant intrapartum hypoxia. Recent findings indicate that only when cord artery pH falls below 7.0 and when there is substantial metabolic acidemia is there a significant risk of intrapartum asphyxia. Metabolic acidemia should be estimated from base deficit in the extracellular fluid and the combination of cord artery and vein data should allow for a more accurate assessment of intrapartum events, including the assessment of the duration of hypoxia. The Plymouth trial has tested the hypothesis that the combination of ST wave form and CTG analysis compared with CTG analysis only would reduce operative interventions for fetal distress without placing the fetus at a risk.(ABSTRACT TRUNCATED AT 400 WORDS)

Intrapartum hypoxia was thought to contribute to the incidence of cerebral palsy, seizures and mental retardation. Electronic fetal monitoring was expected to prevent or reduce this incidence. Electronic fetal monitoring has a high false positive rate and fetal blood sampling, which is an invasive procedure, only allows an intermittent assessment. Efforts are being made to improve fetal heart rate analysis and clinical management. Fetal pulse oximetry, fetal electrocardiogram waveform analysis and the intermittent measurement of lactate levels by fetal blood sampling may become established as an adjunct to electronic fetal monitoring.

7.0 Obstetric management

Update on Fetal Monitoring: Overview of Approaches and Management of Category II Tracings

Response to category II tracings: Does anything help?

Intrapartum fetal hypoxia is related to long-term morbidity and mortality of the fetus and the mother. Fetal surveillance is extremely important to minimize the adverse outcomes arising from fetal hypoxia during labour. Several methods have been used in current clinical practice to monitor fetal well-being. For instance, biophysical technologies including cardiotocography, ST-analysis adjunct to cardiotocography, and Doppler ultrasound are used for intrapartum fetal monitoring. However, these technologies result in a high false-positive rate and increased obstetric interventions during labour. Alternatively, biochemical-based technologies including fetal scalp blood sampling and fetal pulse oximetry are used to identify metabolic acidosis and oxygen deprivation resulting from fetal hypoxia. These technologies neither improve clinical outcomes nor reduce unnecessary interventions during labour. Also, there is a need to link the physiological changes during fetal hypoxia to fetal monitoring technologies. The objective of this article is to assess the clinical background of fetal hypoxia and to review existing monitoring technologies for the detection and monitoring of fetal hypoxia. A comprehensive review has been made to predict fetal hypoxia using computational and machine-learning algorithms. The detection of more specific biomarkers or new sensing technologies is also reviewed which may help in the enhancement of the reliability of continuous fetal monitoring and may result in the accurate detection of intrapartum fetal hypoxia.

Intrapartum fetal surveillance

ST Analysis of the Fetal ECG, as an Adjunct to Fetal Heart Rate Monitoring in Labour: A Review.

Intrapartum fetal surveillance

Editor’s choice

PII: S0377-1237(09)80040-3

Electronic fetal monitoring (EFM) involves the use of cardiotocograph (CTG) to asses fetal wellbeing during labour in order to detect intrapartum fetal hypoxia early so as to institute timely and appropriate action. Indeed, when CTG was introduced into obstetric practice in the 1960s, it was expected to prevent perinatal brain injury and reduce the incidence of short term (neonatal admissions, seizures and neonatal deaths) and long term (cerebral palsy, learning difficulties) that arise secondary to intrapartum hypoxic insults. Unfortunately, although the rates of caesarean sections have dramatically increased over the last 40 years, there has been virtually no change in cerebral palsy rates. However, increasing caesarean section rates have contributed to maternal morbidity and mortality, including rising incidence of morbidly adherent placentae (placenta accrete, increta and percreta). Apart from a high 'false positive' rate of CTG, failure to appreciate the pathophysiology of fetal heart rate changes by the clinicians have contributed to increased operative deliveries, without any substantial improvements in neonatal outcomes. Hence, a rational approach is warranted in the use and interpretation of CTGs to improve maternal and fetal outcomes, in all settings, irrespective of the availability of additional tests of fetal wellbeing such as fetal blood sampling (FBS), fetal electrocardiograph (ST analyser or STAN), fetal pulse oximetry or scalp lactate. DOI: <a href="http://dx.doi.org/10.4038/sljog.v32i4.3988">http://dx.doi.org/10.4038/sljog.v32i4.3988</a> <em>SLJOG </em>2010; 32(4): 77-84

Despite advances in fetal monitoring during labor, one of the most critical causes of neonatal death and neurologic injuries remains intrapartum asphyxia. Umbilical cord gases can be used to detect acidosis and fetal distress. We conducted a retrospective, multicenter study to evaluate umbilical cord blood pH and lactate as a mean of evaluating the degree of intrapartum hypoxia and also to establish which of the two is more reliable in predicting morbidity in term neonates. The present study utilized a total of 124 cases that met the criteria for intrapartum asphyxia and 150 normal term newborns that were randomly selected as case control. Both umbilical cord lactate and pH proved to be accurate predictors of neonatal morbidity caused by intrapartum hypoxia. Lactate proved to be superior to pH in predicting adverse neonatal outcome. The greatest sensibility and specificity in predicting intrapartum asphyxia were achieved in our study by using a cutoff value of 3.75 mmol/l for lactate and 7.24 for pH.