Fetal Monitoring in VBAC.
By Melissa Maimann
Caesarean section rates have risen in the past twenty years to a
rate of approximately 20% – 25% in the United States (McMahon, 1998,
p.369). Repeat caesarean section is cited as the most common indication
for caesarean section (McMahon, 1998, p.369). It is hoped that by
promoting vaginal birth after caesarean section, we will halt the
increase in the caesarean section rates (McMahon, 1998, p.369). A
trial of labour should be encouraged after a previous caesarean section,
provided that there are no absolute contraindications to vaginal birth,
such as placenta praevia or cephalo-pelvic disproportion (Wing and
Paul, 1999, p.836). Due to the greater risk of uterine rupture in
women having vaginal births after previous caesarean sections (Menihan,
1999, p.40), it is necessary to monitor the labour to minimise maternal
and fetal mortality and morbidity (McMahon, 1998, p.369). The midwife
plays a vital role in monitoring the well being of woman and fetus
during labour, hence the focus of this options paper will be intrapartum
fetal monitoring for women who have had previous caesarean sections.
It is known that changes in the fetal heart rate may signal an impending
or actual uterine rupture (Menihan, 1999, p.40), so the monitoring
of fetal heart rate is vital to the success of vaginal birth after
caesarean section. There is indecision regarding the most appropriate
method of intrapartum fetal monitoring in women attempting a vaginal
birth after caesarean section owing to a lack of research in the area.
Therefore, I have reviewed the literature regarding fetal monitoring
in high risk women (including vaginal birth after caesarean section),
and fetal monitoring in general. Unfortunately, there is no consensus
as yet; fetal monitoring in labour remains a controversial issue.
Fetal bradycardia may be the first sign of an impending uterine rupture
(Menihan, 1999, p.40). Late decelerations, variable decelerations,
or prolonged decelerations may also occur (Menihan, 1999, pp.40-46).
Furthermore, there is loss of variability, and reactivity may be poor
(Menihan, 1999, pp.40-46). It is important that intrapartum monitoring
enables the detection of these decelerations. The goal of fetal monitoring
in labour is to detect fetal hypoxia early, so that interventions
may be instituted to prevent a neonatal death (Mahomed, Nyoni, Mulambo,
and Jacobus, 1994, p.497; Vintzileos, Nochimson, Guzman, Knuppel,
Lake, and Schifrin, 1995, p.149).
Until the 1960s when the electronic fetal heart rate monitor became
commercially available, intermittent auscultation was the only method
of monitoring the fetal heart rate (Seymour, 1995, p.47). Intermittent
auscultation may be performed by the midwife, using a doppler sonic
aid, or a pinard stethoscope (Seymour, 1995, p.47). Alternatively,
the midwife may monitor the fetal heart rate continuously with an
electronic fetal heart rate monitor, either externally, or internally
with a fetal scalp electrode. Since these methods rely on the interpretation
of changes in the fetal heart rate, it was thought that a more objective
assessment of fetal well being may improve outcomes (McNamara and
Dildy, 1999, p.671; Greene, 1999, p.641). Fetal well being may be
ascertained by obtaining a fetal blood sample and analysing acidity
(pH). This is a medical intervention, and will be evaluated as a method
of fetal monitoring that complements intermittent auscultation. The
remainder of this options paper will describe and evaluate each of
the above-mentioned methods of assessing intrapartum fetal well-being.
Intermittent auscultation involves periodically auscultating the
fetal heart rate. Gilles, Norman, Dawes, Gee, Rouse, and Newnham (1997,
pp.143-148) reviewed methods for intermittent auscultation. They found
no consensus regarding appropriate intervals for auscultating the
fetal heart rate. In first stage labour, recommendations ranged from
auscultation every two hours to every ten minutes, with most sources
advocating auscultation every thirty minutes (Gilles et al., 1997,
p.145). During second stage labour, guidelines for intermittent auscultation
ranged from ‘at intervals’, to every fifteen minutes, to after every
contraction (Gilles et al., 1997, p.145). It was generally accepted
that auscultation should be performed after every contraction. Intermittent
auscultation, as discussed in this options paper, will imply auscultation
every thirty minutes during first stage labour, and after every contraction
during second stage labour.
The pinard stethoscope was invented during the 1800s for the purpose
of auscultating the fetal heart rate (Seymour, 1995, p.47). It is
placed firmly on the woman’s abdomen, at right angles to it, with
the midwife’s ear in close contact with the stethoscope (Bennett and
Brown (eds.), 1999, p.224). The pinard stethoscope is portable and
readily available, and is an excellent tool for monitoring the fetal
heart rate as long as the midwife is confident in interpreting what
is heard (Seymour, 1995, p.47). The only disadvantage of the pinard
stethoscope is that only the listener may hear the heart beat (Seymour,
Mahomed et al. (1994, pp.497-500) conducted a randomised controlled
trial on the effectiveness of different methods of intrapartum monitoring.
They found that abnormalities in the fetal heart rate were more reliably
detected by doppler sonic aid, compared with a pinard stethoscope.
They also found that auscultation with the pinard stethoscope was
uncomfortable for the woman as it sometimes required a change of position,
and that the woman remain still during auscultation (Mahomed et al.,
1994, pp.497-500). Lower apgar scores were more common in the groups
monitored with the pinard stethoscope, and neonatal seizures occurred
only in the groups monitored with the pinard stethoscope (Mahomed
et al., 1994, pp.497-500).
During the late first stage and second stage of labour, contractions
are the longest and strongest; theoretically, this period poses the
greatest risk of uterine rupture (Arulkumaran, Gibb, Ingermasson,
Kitchener, and Ratnam, 1989, cited in Chua and Arulkumaran, 1997,
p.7). Anecdotal evidence suggests that auscultation of the fetal heart
rate with a pinard stethoscope is often difficult to perform at this
time, as the baby has descended into the pelvis. This makes intermittent
auscultation difficult to perform, at a time when uterine rupture
and possible fetal heart rate abnormalities are the most likely to
present. For these reasons, women attempting vaginal birth after caesarean
section are best not monitored with the pinard stethoscope as the
main method of fetal monitoring.
The doppler sonic aid is the electronic equivalent of the pinard
stethoscope, and has the advantage of enabling the woman to hear her
baby’s heart beat (Seymour, 1995, p.47). It is possible to auscultate
the fetal heart rate with the woman in any position, and there are
waterproof probes available for use in the shower or bath (Steer,
1999, p.858). In their study, Mahomed et al. (1994, pp.497-500) found
that detection of fetal heart rate abnormalities was better with the
doppler sonic aid than with the pinard stethoscope, and that the perinatal
outcome was no worse than that achieved by intermittent electronic
The American College of Obstetricians and Gynecologists (1989, cited
in Cibils, 1996, p.1382) recommends that intermittent auscultation
and continuous electronic fetal monitoring are equally acceptable
methods of fetal monitoring, even in high risk labours. In a Birth
Centre study of vaginal birth after caesarean section, Harrington,
Miller, McClain, and Paul (1997, pp.304-307) used intermittent auscultation
as the main form of fetal monitoring. It was performed during at least
one contraction, every fifteen minutes. In both the study and control
groups, the average apgar scores were 8.5 at one minute, and 9 at
five minutes, and no five minute apgar scores were less than seven
(Harrington et al., 1997, p.306). Neonatal outcomes were similar among
both study and control groups (Harrington et al. 1997, p.306). These
studies demonstrate the safety and acceptability of intermittent auscultation
to monitor the fetal heart rate in women attempting a vaginal birth
after caesarean section.
Generally, the literature supports intermittent auscultation as a
safe method of fetal heart rate monitoring. Enkin, Kierse, Renfrew,
and Neilson (1995) conclude that intermittent auscultation is just
as effective in preventing intrapartum death as continuous electronic
monitoring. Thacker, Stroup, and Peterson (1995, pp.613-620) studied
the efficacy and safety of electronic fetal monitoring, and found
that neurological consequences occurred in similar frequencies in
babies monitored by intermittent auscultation and continuous electronic
monitoring. Kripke (1999, p.2421) describes intermittent auscultation
as a “high touch, low-tech” method of lowering the caesarean section
rate for fetal distress. Gilles et al. (1997, p.147) suggest that
intermittent auscultation may also play an important role in neonatal
outcome, as the personal support provided by a midwife during intermittent
auscultation of the fetal heart rate may contribute to reduced pain
relief requirements and improved progress of labour. These are important
aspects of the care of a woman attempting a vaginal birth after caesarean
To conclude the literature review of intermittent auscultation, use
of the doppler sonic aid improves neonatal outcomes when compared
with the pinard stethoscope. Literature comparing use intermittent
auscultation and continuous fetal monitoring, even for high risk labours,
concludes that intermittent auscultation is at least as effective
in preventing neonatal morbidity and mortality. Current and accepted
recommendations are for the fetal heart rate to be auscultated every
thirty minutes (minimum) in the first stage of labour, and after every
contraction in the second stage of labour.
The alternative to intermittent auscultation is to continuously monitor
the fetal heart rate internally via a fetal scalp electrode, or externally
via doppler ultrasound (Bennett and Brown, 1999, pp.418-419). A tocotransducer,
strapped to the fundus of the uterus, is also used to monitor the
frequency, intensity, and duration of uterine contractions (Bennett
and Brown, 1999, pp. 418-419). This form of monitoring is known as
cardiotocography (CTG), and the electronic fetal monitor produces
a print-out of fetal heart rate in relation to uterine contractions.
The fetal heart response to contractions (and fetal movements) is
monitored to determine fetal well being in labour (Bennett and Brown,
1999, p.418). Continuous fetal monitoring was introduced with the
hope of detecting early signs of fetal compromise, enabling early
intervention to reduce neonatal mortality and morbidity (Boehm, 1999,
p.623; Parer and King, 2000, p.982).
Continuous fetal monitoring was seen as an important development
in the reduction in neonatal mortality and morbidity, however, proponents
of CTG failed to acknowledge the contribution that improved antenatal
and neonatal intensive care have made to neonatal well being (Dover
and Gauge, 1995, p.18).
In fact, it has been suggested that CTG, as a screening tool, has
been far from beneficial for most women. There is a lack of agreed
interpretation of fetal heart rate traces (Anonymous, 1997, p.1385;
Low, 1999, p.725), with the result of increased intervention in the
form of caesarean section and forceps deliveries (Boehm, 1999, p.623).
The adverse effects of false positive and false negative CTGs suggests
that, as a screening tool for fetal distress in labour, the CTG fails
miserably (Low, 1999, p.725).
A study conducted by Vintzileos, Nochimson, Antsaklis, Varvarigos,
Guzman, and Knuppel (1995, pp.1021-1024) suggested that CTG was superior
to intermittent auscultation in detecting fetal acidaemia at birth.
This conclusion was correct, however, the authors failed to state
the false positive rate of CTG in their study, as opposed to intermittent
auscultation. Cibils, (1996, p.1383) states that over 40% of fetal
heart rate patterns are abnormal on CTG, yet Vintzileos, Nochimson,
Antsaklis et al. (1995, pp.1021-1024) found that only 8.0% of neonates
had acidaemia at birth. Although CTGs were able to accurately detect
changes in the fetal heart rate suggestive of acidaemia, there must
have also been a substantial number of fetal heart traces suggestive
of acidaemia that were in fact perfectly normal. A meta-analysis by
Vintzileos, Nochimson, Guzman, et al. (1995, pp.149-155), found that
one perinatal death may be prevented by the continuous fetal monitoring
of one thousand women in labour (p.154). The authors accept that this
would occur at the expense of a higher rate of surgical intervention.
A benefit of continuous CTG monitoring in labour is a reduction in
neonatal seizures (Greene, 1999, p.647; Boehm, 1999, p.625) and one
minute apgar scores of less than four (Thacker, Stroup, and Peterson,
1995, p.615). However, the authors of these articles conclude that
the long term effect of this reduction must be balanced against the
increase in caesarean and operative vaginal delivery rates (Thacker
et al. 1995, p.619; Boehm, 1999, p.623; Greene, 1999, p.647).
Wing and Paul (1999, p.843) and Scott (1997, p.536) advocate continuous
CTG monitoring for women planning a vaginal birth after caesarean
section because abnormal fetal heart rate traces are the most common
signs of uterine rupture. The incidence of uterine rupture among women
planning a vaginal birth after caesarean section is quoted at being
between 0.3% and 1.7% (Chua and Arulkumaran, 1997, p.6). Fetal heart
rate abnormalities occur in 50%-70% of uterine ruptures (Scott, 1997,
p.538), but they also occur in at least 40% of labours with an unscarred
uterus (Cibils, 1996, p.1383). The literature failed to address how
the midwife or doctor may distinguish fetal distress related to uterine
rupture, requiring emergency caesarean section, from fetal heart rate
abnormalities resulting from occurrences such as cord compression
or head compression (Menihan, 1999, p.45). In fact, Menihan (1999,
p.40) states that there is ‘no single, specific change in fetal heart
rate (FHR) pattern predictive of uterine rupture prior to the onset
of a profound bradycardia’. Furthermore, since abnormal CTG patterns
alone cannot accurately distinguish well fetuses from distressed fetuses,
I question the accuracy of this form of monitoring in women planning
vaginal births after caesarean sections.
A review of the literature suggests that continuous fetal monitoring
affords no overall benefit; the reduction in neonatal seizures and
low one minute apgar scores occurs at the expense of increased operative
deliveries. The options presented thus far are not sufficient enough
to conclude that intermittent auscultation is the safest method of
fetal monitoring in the woman attempting a vaginal birth after caesarean
section. These women require closer monitoring than intermittent auscultation
can provide, however, they may suffer unnecessary intervention from
the use of continuous monitoring. A compromise is needed.
Fetal blood sampling to ascertain pH (acidity) was developed in the
1960s with the aim of clarifying uncertain CTG patterns (Greene, 1999,
p.641). On the basis of CTG patterns alone, false-positive diagnoses
of fetal distress are likely to be made (Greene, 1999, p.645). A meta-analysis
demonstrated that without access to fetal blood sampling, women who
were monitored continuously experienced a four-fold increase in caesarean
section rates compared with intermittent auscultation, with no improvement
in fetal outcome (Greene, 1999, p.647). When fetal blood sampling
was used in conjunction with continuous monitoring or intermittent
auscultation, this rise in caesarean section rates was less marked
(Greene, 1999, p.647). It is essential that all forms of fetal monitoring
be supplemented by fetal blood sampling where indicated, to reduce
unnecessary intervention (Steer, 1999, p.859).
Fetal blood sampling has some disadvantages: it is time-consuming
to perform (Steer, 1999, p.859), it is unreliable if performed in
the presence of oedema or caput succedaneum, and it can only be performed
intermittently (Greene, 1999, p.648). However, when it is indicated
it may accurately determine fetal acid-base balance in fetuses suspected
of compromise on intermittent auscultation of the heart rate. Therefore,
it may either confirm the diagnosis of fetal distress, or reassure
care givers of fetal well being. Although it is not part of the midwifery
management of fetal monitoring, it is capable of complementing intermittent
auscultation in women planning vaginal births after previous caesarean
sections, thus increasing the safety of vaginal birth after caesarean
section, without increasing intervention rates unnecessarily.
In conclusion, the midwifery management of fetal monitoring in women
planning vaginal births after caesarean sections is controversial.
Standard practice is to continuously monitor the labour using technology
that is known to increase operative delivery rates with no proven
benefit. On the basis of a literature review, this paper has presented
the available options of fetal monitoring. The evidence suggests that
even without access to fetal blood sampling, intermittent auscultation
is superior to continuous monitoring in correctly identifying fetuses
in need of immediate delivery. In the presence of an abnormal fetal
heart rate detected by intermittent auscultation, fetal blood sampling
may indicate those fetuses that require immediate delivery, or reassure
the midwife of fetal well being. Ultimately, the woman needs to be
informed of her options for care, and their relative risks and benefits,
as she will be the one to experience and live with the consequences
(positive or negative) of labour care. This options paper is only
a guide, based on the conflicting literature available at this time.
Since we cannot say with 100% certainty that one method of monitoring
is superior over another, perhaps midwives could best care for women
by providing accurate information that facilitates involvement and
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