Use of Fetal Monitoring
Fetal 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 fetal blood sampling (FBS). It does
however provide a continuous visual record that includes variability and is highly
sensitive for fetal distress, reducing short term neurological morbidity, and hopefully
allaying fears for the anxious parents. The disadvantages are than it restricts maternal
movement and has a 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 fetal monitoring should be used is via a simple
schematic as below.
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Level 1:- 20 minute admission CTG for all women then intermittent auscultation
of the fetal 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:- Fetal Blood Sampling. If abnormal proceed to:Level 4:- Delivery via quickest possible route.
All of the above forms of fetal monitoring will be discussed in this website along with
their interpretation.
Fetal Distress
What is fetal distress?
Fetal distress is the term commonly used to describe fetal hypoxia. It is a clinical
diagnosis made by indirect methods and should be defined as:Hypoxia that may result in fetal damage or death if not reversed or the fetus delivered
immediately.
More commonly a fetal scalp pH of less than 7.2 is used to indicate distress (1)(2).
What can cause Fetal Distress?
There are potentially limitless causes for fetal distress but several key mechanisms are
usually involved. Contractions reduce temporarily placental blood flow and can compress
the umbilical cord. If a women is in labour longer then this can cause fetal distress via the
above mechanism (1)(3).
Acute distress can be a result of placental abruption, prolapse of the umbilical cord
(especially with breech presentations), hypertonic uterine states and the use of oxytocin
(1).
Hypotension can be caused by either epidural anaesthesia or the supine position, which
reduces inferior vena cava return of blood to the heart. The decreased blood flow in
hypotension can be a cause of fetal distress (1).
Which babies are at risk of Fetal Distress?
Any baby can run the risk of becoming distressed but there are indications for increased
fetal monitoring. Long labour, the presence of Meconium and the use of epidurals or
oxytocin all would suggest the need for more monitoring (1)(2)(3).
Meconium
Meconium is the bowel contents of the fetus which has stained the amniotic fluid. In preterm fetuses it is rare but is present in 30% of cases after 42 weeks (1).
If the meconium is old or dilute it is seldom significant but if it is thick or undiluted then
it is often passed in response to hypoxia and then perinatal death is increased four-fold
(1). A breech positioned baby may well lead to the observation of thick undiluted
meconium but if the baby is cephalic oligohydramnios may be the cause and if the
Cardiotocography (CTG) trace is suspicious the baby should be delivered (2)(3).
Because meconium can be passed under normal circumstances its presence or absence is
not a reliable indicator. In addition the presence of the head in the pelvis might prevent it
from being revealed as would a late amniotomy(1).
Caution is indicated if it is present however because:
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The fetus might aspirate it causing meconium aspiration syndrome.
Hypoxia is more likely.
If meconium is present Cardiotocography (CTG) is indicated (2).
Cardiotocography
Introduction | Baseline Rate | Baseline Variation | Accelerations | Decelerations
Introduction:- A Cardiotocograph (CTG) is a record of the fetal heart rate (FHR) either
measured from a transducer on the abdomen or a probe on the fetal scalp. In addition to
the fetal heart rate another transducer measures the uterine contractions over the fundus
(1).
Diagram showing the CTG in use. Adapted from (4)
The interpretation of a cardiotocograph is complicated but this site will aim to
demonstrate some of the more straightforward characteristics a CTG may display. The
CTG trace generally shows two lines. The upper line is a record of the fetal heart rate in
beats per minute. The lower line is a recording of uterine contractions from the toco. The
vertical scale of this trace depends on how the transducer is picking up the contractions
so interpretation needs to be in relation to the rest of the trace. The trace may also have
markings on it that are indications that the mother has felt a fetal movement (operated by
a switch given to the mother) (5)(6).
The following section describes the different patterns seen on a CTG. The example
CTG's were kindly obtained from Nigel Simpson at the Department of Obstetrics and
Gynaecology, University of Leeds, England (7).
Introduction | Baseline Rate | Baseline Variation | Accelerations | Decelerations
Baseline Rate:- This should be between 110 and 150 beats per minute (BPM) and is
indicated by the FHR when stable (with accelerations and decelerations absent). It should
be taken over a period of 5 - 10 minutes. The rate may change over a period of time but
normally remains fairly constant (5)(1).
This is a section of CTG showing a typical normal baseline rate (7).
Bradycardia:- This is defined as a baseline heart rate of less than 110 bpm. If between
110 and 100 it is suspicious whereas below 100 it is pathological. A steep sustained
decrease in rate is indicative of fetal distress and if the cause cannot be reversed the fetus
should be delivered (1)(5)(6).
This is a section of CTG showing a bradycardia (7).
Tachycardia:- A suspicious tachycardia is defined as being between 150 and 170
whereas a pathological pattern is above 170. Tachycardias can be indicative of fever or
fetal infection and occasionally fetal distress (with other abnormalities). An epidural may
also induce a tachycardia in the fetus (1).
This is a section of CTG showing a tachycardia (7).
Introduction | Baseline Rate | Baseline Variation | Accelerations | Decelerations
Baseline variations:- The short term variations in the baseline should be between 10 and
15 bpm (except during intervals of fetal sleep which should be no longer than 60
minutes). Prolonged reduced variability along with other abnormalities may be indicative
of fetal distress (1)(6).
This is a section of CTG showing decreased baseline variability (7).
Introduction | Baseline Rate | Baseline Variation | Accelerations | Decelerations
Accelerations:- This is defined as a transient increase in heart rate of greater than 15
bpm for at least 15 seconds. Two accelerations in 20 minutes is considered a reactive
trace. Accelerations are a good sign as they show fetal responsiveness and the integrity of
the mechanisms controlling the heart (5)(6).
This section of CTG shows a typical acceleration in response to stimulus (7).
Introduction | Baseline Rate | Baseline Variation | Accelerations | Decelerations
Decelerations:- These may either be normal or pathological. Early decelerations occur at
the same time as uterine contractions and are usually due to fetal head compression and
therefore occur in first and second stage labour with decent of the head. They are
normally perfectly benign. Late decelerations persist after the contraction has finished
and suggest fetal distress. Variable decelerations vary in timings and shape with respect
to each other and may be indicative of hypoxia or cord compression (1)(5).
The following CTGs show examples of early, late and variable decelerations (7).
A normal CTG is a good sign but a poor CTG does not always suggest fetal distress. A
more definitive diagnosis may be made from fetal blood sampling but if this is not
possible or there is an acute situation (such as a prolonged bradycardia) intervention may
be indicated (1)(5)(6).
Last modified 21st January 2001
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Blood Sampling
Fetal Blood Sampling (FBS) is a useful tool for the diagnosis of fetal distress. The fetal
scalp is first visualised with an amnioscope inserted vaginally and the scalp is cleaned.
The sample is taken form a small cut made in the scalp from which blood is collected in a
microtube (1)(2).
Fetal Blood Sampling. Adapted from (1).
The blood sample should be immediately analysed for pH and base excess. If the pH is
less than 7.2 there is significant hypoxia and the baby should be delivered by the fastest
means possible (1)(2).
Questions
Question 1
By the time a fetus has reached term (40 weeks) it is usual for Meconium to have been
passed.
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True
False
Question 2
Intermittent auscultation best detects abnormalities if used before each contraction.
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True
False
Question 3
Fetal Blood Sampling shows significant hypoxia if the recorded pH is less than 7.2.
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True
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False
Question 4
The above CTG (7) shows features of:
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a) Decreased Baseline Variation.
b) Accelerations.
c) Sustained bradycardia.
Question 5
The above CTG (7) shows features of:-
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a) Early decelerations.
b) Late decelerations.
c) Variable decelerations.
Question 6
The above CTG (7) shows features of:
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a) Tachycardia.
b) Bradycardia.
c) Decreased Baseline variation.
Question 7
The above CTG (7) shows features of late decelerations.
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True
False
Question 8
The above CTG (7) is normal overall showing only accelerations.
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True
False
Question 9
Which of the following actions would be appropriate for a patient where fetal heart rate
decelerations have been heard with a Pinards stethoscope.
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a) Trying to hear the same decelerations with a sonicaid.
b) Placing the patient on a CTG machine.
c) Taking a fetal blood sample to diagnose distress.
Question 10
On the CTG trace which of the following pieces of information can not be determined.
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a) The relationship between the contractions and the fetal heart rate.
b)The number of contractions in a given time period.
c) The absolute force of the contractions.
Last modified 21st January 2001
E-mail Webmaster