Foetal monitoring is defined as monitoring the baby's heart rate for indicators of stress,
usually during labour and birth using ultrasound and electrocardiography.
A little history
Analysis of the foetal heart sound has been used for over 100 years to find out whether the foetus is alive or not. Pinard´s stethoscope (simple wooden funnel) can still be used for this purpose. Electronic foetal monitoring was introduced during the 1970s with the advent of CTG (cardiotocography). It was recognised that the capability continually to monitor the reactions of the foetus by means of a more detailed foetal heart rate analysis offered entirely new opportunities for the identification of oxygen deficiency and thus the prevention of brain damage. CTG provides information on foetal heart rate and the mothers labour.
This is a special type of stethoscope used for listening to a baby. There are many types of echoscopes available, and a regular stethoscope works as well. This can usually be used after about 18 weeks. This method is non-invasive, simple to use, and has a live person on the other end (This can prevent some of the errors that are mechanical). This gives mother the mobility to deal with her labour, shower, etc. It does require that the person using it be trained, although it is a standard procedure taught in every medical and nursing type institution. In the case of high risk, induced, or with certain medications, it cannot provide the round the clock monitoring that may be necessary.
This is a handheld ultrasound device that transmits the sounds of the baby's heart rate either through a speaker or into ear pieces that are attached. This can generally pick up heart tones after 12 weeks gestation. This method is also used intermittently, requires little training to use, has a live person on the other end, and allows mother to maintain her mobility. It may also be easier to use during a contraction. This device does use ultrasound and does not provide the continuous monitoring needed for high risk labours.
Heart rate traces
The visual assessment of an antepartum foetal heart rate (FHR) trace requires a trained individual to look at the trace, mentally fit a baseline to it, and then ask a number of questions: Are there any accelerations? Is the basal heart rate okay, and does the trace have good variability? Or are there decelerations? Is the basal heart rate too high or too low, or does the trace look a bit flat?
Depending on the answers to these questions an opinion is formed as to whether the trace is reassuring or a cause for concern. In most cases this is sufficient because the baby is fine. But subjective assessments such as these are intrinsically unreliable and problems can, and sometimes do, arise. The person assessing the trace may be tired, stressed, or inexperienced. Misinterpreting traces can lead to intervention when it is not needed or, worse still, no intervention when it is urgently needed. There is no doubt that looking at a trace and forming an opinion of it is useful.
Electronic Foetal MonitoringThe foetal monitor a device used during labour and birth, or during certain testing (non-stress test, contraction stress test, etc.) to record the baby's heart rate, and sometimes mother's contractions. It can be used intermittently or continuously. This type of foetal monitoring is usually carried out in birthing facilities. Electronic Foetal Monitors are used to detect and trace the foetal heart rate and uterine contractions. These are usually monitored at the same time however, each one can be obtained separately. In terms of electronic foetal monitoring, it is either external or internal. Electronic foetal monitoring is a valuable tool for measuring foetal well being and assessing labour progress. Due to the sensitivity of the monitor, it may indicate a contraction is diminishing even before you notice the pain subsiding. This information can be a very useful energy saving tool and source of encouragement for the mother/parents.
External Foetal MonitoringExternal Foetal Monitoring monitors the baby's heartbeat by placing a small round ultrasound (high-speed sound waves) disc with ultrasound gel on the mothers abdomen and held in place by a lightweight stretchable band or belt. Uterine contractions are recorded from a pressure-sensitive transducer that is also placed on the abdomen and held by a lightweight stretchable band or belt. External monitoring of contractions in this manner only tells how often the contractions are occurring and how long each is lasting, but not their actual strength.
Internal Foetal MonitoringThis is more accurate than the external electronic monitoring, does not use ultrasound, and can provide continuous monitoring for the high-risk mother. This method requires that the mothers waters be broken (An amniotomy will be performed if the mothers waters are still intact), and she is 2-3 centimetres dilated. Amniotomy adds risks of its own. However, the risks and benefits of each procedure must be weighed. This type of monitoring is almost exclusively used in high-risk situations or when more accurate types of monitoring may prevent other unnecessary interventions. This type of monitoring also has been associated with foetal injury (from the electrode), infection for mother or baby, etc This is more accurate than the external electronic monitoring, does not use ultrasound, and can provide continuous monitoring for the high-risk mother. This method requires that the mothers waters be broken (An amniotomy will be performed if you water is still intact.), and she is 2-3 centimetres dilated. Amniotomy adds risks of its own. However, the risks and benefits of each procedure must be weighed. This type of monitoring is almost exclusively used in high-risk situations or when more accurate types of monitoring may prevent other unnecessary interventions. This type of monitoring also has been associated with foetal injury (from the electrode), infection for mother or baby, etc.
ST technology is based on a combined analysis of the foetal heart rate and changes in the waveform of the foetal ECG ("ST analysis"). The ECG signal is available during delivery from the scalp electrode.
The analysis is based on the capacity of the ST interval to reflect the condition of the heart muscle under load, for example in an exercise test for adults. Delivery can be regarded as an exercise test for the foetus, and we know with certainty that ST analysis does provide information about the capacity of the foetal heart to respond.
In the foetus, the heart and brain are equally sensitive to hypoxia, which is the form of oxygen deficiency in which the tissues are affected. This means that the heart function can be used as an index of how the brain is coping during delivery. An advanced digital signal processing concept makes it possible to obtain a clear and complete image of the foetal ECG, and so to analyse the ST interval.
Telemetry MonitoringTelemetry Monitoring is a lot like the regular Electronic Foetal Monitoring, however, the mother can maintain mobility. This is the "newest" type of monitoring available. It uses radio waves, connected to a transmitter on the thigh, to transmit the baby's heart tones to the nurses station. The mother maintains her mobility, and has constant monitoring, but again, continuous monitoring for the low risk mother is very questionable in benefit.
Oxygen DeficiencyOxygen deficiency during delivery is one cause of neurological injury in children. The aim of foetal monitoring is to make it possible to identify and quantify the risk of foetal injury, and if necessary to operate in time. The idea is to carry out operative procedures only when necessary, and not merely for safety´s sake. Severe asphyxia, leading to neurological injury or stillbirth, is rare, and many healthy foetuses must be monitored if those affected are to be identified. However, the consequences of injury to the child are so far-reaching not only on a humanitarian but also on a social and financial level that we must continue to attempt to diagnose severe asphyxia with all means at our disposal.
Problems with Standard Practices of Foetal MonitoringThe problems with standard foetal monitoring are that we tend to want to use continuous foetal monitoring on everyone. However, today we know that in most cases, routine continuous foetal monitoring of every woman does not improve foetal or maternal outcomes, it only tends to increase the caesarean rates. We have found that using a foetoscope or doppler is just as effective in predicting foetal well-being.
How long should we monitor for?From about 28 weeks gestation a healthy foetus cycles between episodes of active and quiet sleep. Active sleep is associated with accelerations, increased FHR variation and clusters of foetal movements, so the appearance of these features - a reactive trace - is a primary indication of foetal wellbeing. Quiet sleep is associated with reduced variation and reduced foetal movements, so during quiet sleep it is not possible to assess foetal wellbeing. This is because the non-reactive trace of a healthy foetus in quiet sleep is indistinguishable from the trace of a compromised foetus. To make the distinction monitoring must continue until a time when we would expect to see the appearance of a reactive trace, but this time will vary depending on the point in the foetal sleep cycle at which monitoring begins. Episodes of quiet sleep can last for up to 50 minutes, so if the start of monitoring coincides with the start of quiet sleep it may be up to 50 minutes before a reactive trace starts to appear. However, if the same foetus is monitored again later the same day it may already be in active sleep and a 10-15 minute trace will be sufficient to confirm reactivity. A study of over one thousand traces concluded that a reactive trace is indicative of foetal wellbeing irrespective of the time required to detect reactivity, up to a limit beyond which it becomes abnormal that the trace is not reactive. In foetal care this limit is usually set to 60 minutes for the reasons given above.
Foetal monitoring provides a window allowing the midwife or doctor to see how the unborn child is faring. Whilst there may be a temptation to monitor everything possible continuously this is seldom necessary in low risk pregnancies progressing normally. Cardiotocography (CTG) is a useful tool but suffers from problems caused by poor interpretation, inappropriate timing or lack of foetal blood sampling (FBS). The problem has been that the CTG pattern in cases of hypoxia (serious oxygen deficiency that affects the body tissues) is insufficiently specific.
It does however provide a continuous visual record that includes variability and is highly sensitive for foetal distress, reducing short-term neurological morbidity, and hopefully allaying fears for the anxious parents. Many deliveries are interrupted because of the danger of foetal asphyxia (the most serious form of oxygen deficiency, which affects central organs), without any genuine symptoms of oxygen deficiency being present. There are many different reasons for changes in foetal heart rate, most of which have nothing to do with oxygen deficiency but result from entirely normal changes in the foetus and its environment. CTG patterns that deviate from the norm therefore occur in about half of all deliveries, and overreaction to these commonly-occurring heart rate changes is frequent, leading to many and unnecessary intervention in the form of acute caesarean section and forceps or ventouse delivery.
All this has given rise to uncertainty concerning the value of CTG, and the worst consequence of this is that genuinely pathological CTG patterns - i.e. foetuses suffering serious oxygen deficiency - may be overlooked, resulting in injury to the child. Generally speaking, it might be said that CTG is better at identifying a normal condition than at diagnosing and classifying anomalies, and therefore works best as a screening method, i.e. as a way of verifying that everything is normal.
The disadvantages are than it restricts maternal movement and has a lower specificity with an increased rate of obstetric intervention. There is also no proven reduction in mortality or long term handicap when CTG is used.
One way of deciding what form of foetal monitoring that may be used is as below:
Level 1:- 20 minute admission CTG for all women then intermittent auscultation of the foetal heart if everything normal. If either abnormal or if meconium, or if long or high risk labour proceed to:-
Level 2:- Continuous CTG. If sustained bradycardia then deliver. If other abnormalities proceed to:-
Level 3:- Foetal Blood Sampling. If abnormal proceed to:-
Level 4:- Delivery via quickest possible route.
Foetal monitoring provides reassurance to the mother and extra information to the clinicians and midwives, but is a device that requires training and experience to make it a source of reliable information. There are many incidences of misinterpretation from these devices and it is important that users are aware of the limitations involved when using these devices.
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Compiled and Edited by John Sandham IEng MIET MIHEEM