SMJ 2003 49(1): 22-25
Nicoll AE, Black C, Powls A, Mackenzie F.
Princess Royal Maternity Hospital, 16 Alexandra
Parade, Glasgow, G31 2ER.
Abstract:
Background:
Studies have suggested that a reduction in neonatal respiratory morbidity
may be achieved by delaying elective caesarean section until 39 weeks gestation.
In 1997 staff at the Glasgow Royal Maternity Hospital were concerned at
the level of neonatal respiratory morbidity following elective caesarean
section.
Aims: To determine the extent of neonatal respiratory morbidity
following elective caesarean section at term.
Then to present the findings, make recommendations and perform a repeat
analysis.
Methods: A retrospective analysis of all elective caesarean sections
at term between October 1996 and October 1997 was performed.
Labour ward, operating
theatre and SCBU records were examined, followed by maternal and infant case
note review. The
gestational age at the time of caesarean section and any neonatal respiratory
morbidity was recorded. The results were subsequently presented at a perinatal
morbidity meeting and a recommendation made to delay elective sections until 39
weeks gestation. The audit was
repeated between June 1999 and June 2000.
Results: The first cycle of the audit showed significantly lower rates
of neonatal admissions with advancing gestation (p < 0.001). There was also a
reduction in the number of infants requiring oxygen (p = 0.001), the number of
infants requiring intensive care admission (p=0.001) and ventilation (p = 0.003)
with advancing gestation.
In
the second cycle of the audit there was a significant decrease in the number of
elective caesarean sections performed prior to 39 weeks gestation (51% vs. 26%)
(p < 0.0001). There were fewer
neonatal admissions with respiratory morbidity between the two phases of the
audit (26/292 vs. 18/327) (RR = 0.62, 95%CI 0.34 - 1.1).
There was also a reduction in the number of infants requiring oxygen (RR
= 0.5, 95% CI 0.23 - 1.06) the number of infants requiring intensive care
admission (RR = 0.45, 95% CI 0.15 - 1.29) and the number of infants requiring
ventilation (RR = 0.38, 95% CI 0.1 - 1.47).
Conclusion: A reduction in neonatal respiratory morbidity can be achieved
by delaying elective caesarean section until 39 weeks gestation.
Introduction:
The
establishment of lung function at birth is dependent upon removal of fluid that
fills the fetal lungs in utero, the institution and maintenance of a functional
residual capacity and the development of a ventilation-perfusion relationship
that allows successful gas transfer between the alveoli and the circulation.
These changes occur within the first few seconds of life as the newborn
infant begins to breathe. Any
disruption to this complex physiological process can cause neonatal respiratory
distress.
Despite
appropriate gestational age it is well recognised that infants delivered by
caesarean section have significantly greater respiratory morbidity than those
delivered vaginally 1, 2, 3, 4, 5.
The timing of elective caesarean section would appear to be a crucial
factor in the prevention of neonatal respiratory illness.
Delaying elective caesarean section until 39
weeks gestation can reduce neonatal respiratory morbidity1.
In
1997 at the Glasgow Royal Maternity Hospital obstetric and paediatric staff were
concerned that a significant number of neonates were being admitted to the
Special Care Baby Unit with respiratory distress following elective caesarean
section. Therefore an audit of
respiratory illness in neonates following delivery by elective caesarean section
was conducted.
Methods:
A
retrospective audit of infants delivered by elective caesarean section was
conducted. The aims of the audit
were:
To
identify gestations at which elective caesarean section were being
performed.
To
identify extent of neonatal respiratory morbidity.
To
compare levels of neonatal morbidity with other published figures.
To
present the findings, make recommendations for future practice.
Re-audit
to establish whether or not practice had changed.
Information
regarding deliveries at the Glasgow Royal Maternity Hospital between October
1996 and October 1997 was obtained. The
labour ward register of births and the operating theatre books were used to
identify those women who had been delivered by elective caesarean section.
An elective caesarean section was defined as one with which the timing of
delivery could be postponed, i.e. one in which prolonging the pregnancy would
not pose risks to the mother or fetus. The
admission book for the Special Care Baby Unit was then examined to identify
those infants who had been admitted to the unit following delivery by elective
caesarean section.
The
maternal and infant case records were then analysed and the relevant information
was extracted. From the maternal
notes, information was gathered about the gestation at which the operation was
performed; the estimated date of delivery being the first day of the woman’s
last menstrual period + 280 days. An
ultrasound scan was performed before 20 weeks gestation to confirm gestational
age. If there was a discrepancy of
greater than 1 week then the estimated date of delivery was calculated using
ultrasound measurements.
From
the infant records information was obtained about the respiratory illness and
the duration of stay in the neonatal unit.
The respiratory diagnosis was based on serial chest radiographs and
clinical course. Information was obtained on oxygen and ventilation requirements
and their duration.
The
results of the first audit cycle were presented to obstetric and paediatric
staff at the Glasgow Royal Maternity Hospital in January 1998 at a perinatal
meeting. At this time obstetric
staff were recommended to delay elective caesarean section until 39 weeks
gestation unless there was a clear obstetric indication to deliver earlier.
No other specific action was taken to ensure compliance with this
recommendation. The audit was then
repeated, examining elective caesarean deliveries at the Glasgow Royal Maternity
Hospital between June 1999 and June 2000.
Statistical
analysis was performed using MinitabTM
for Windows version 13. Linear
regression models were used to analyse the effects of gestation at the time of
delivery on the frequency of neonatal respiratory illness.
Mann-Whitney and Fishers Exact Tests were used to compare the 2 groups.
A p-value of less than 0.05 represented statistical significance.
Results:
Cycle
1 (1996 - 1997):
Between
October 1996 and October 1997 there were 4409 live-births at the Glasgow Royal
Maternity Hospital. Of these 292
(6.6%) infants were delivered by elective caesarean section. 51%
of elective caesarean sections were performed at a gestational age of less than
39 weeks. 26 (8.8%) infants required admission to the neonatal unit with respiratory
illness following elective caesarean delivery (Table I).
The median duration of time spent in the neonatal unit was 5.5 days
(range 2 - 20 days).
In
the first audit cycle one infant was admitted to the neonatal unit with TTN
following delivery by elective caesarean section at 39 weeks gestation. This infant remained on the unit for 47 days because of
failure to thrive and poor feeding, which were not related to its initial
respiratory illness. As this tended
to severely skew the data for duration of stay, this figure was omitted from the
analysis.
There was a reduction in the number of neonatal
admissions with respiratory morbidity with advancing gestation (p < 0.001) (Table
I / Figure I).
Increasing gestational age at the time of elective caesarean section was
associated with a significant reduction in the number of infants requiring
oxygen (p = 0.001), the number of infants requiring intensive care admission
(p=0.001) and the number of infants requiring ventilation (p = 0.003) (Figure
I).
Cycle
2 (1999 - 2000):
Between
June 1999 and June 2000 there were 4829 live-births at the Glasgow Royal
Maternity Hospital. Of these 327
(6.8%) infants were delivered by elective caesarean section.
26% of elective caesarean sections were performed
< 39 weeks, a reduction of 25% compared to the first audit cycle (p <
0.0001) (Figure II).
18 (5.5%) infants required
admission to the neonatal unit with respiratory illness following elective
caesarean delivery (Relative Risk = 0.62, 95% CI 0.34 - 1.1) (Table II).
The
median duration of time spent in the neonatal unit was 5 days (range 2 - 12
days). In the second audit cycle
one infant was admitted to the neonatal unit with respiratory distress following
delivery by elective caesarean section at 39 weeks gestation. This infant remained on the unit for 43 days because of
breathing and feeding difficulties secondary to Pierre-Robin Sequence.
Again this tended to skew the data for duration of stay, and this figure
was therefore omitted from the analysis.
There was a reduction in the number of infants requiring oxygen (RR = 0.5, 95% CI 0.23 - 1.06) the number of infants requiring intensive care admission (RR = 0.45, 95% CI 0.15 - 1.29) and the number of infants requiring ventilation (RR = 0.38, 95% CI 0.1 - 1.47) compared to the first audit cycle (Figure III). However , none of these differences were statistically significant.
Discussion:
Morrison et al 1 reported that the lowest rates for neonatal
respiratory morbidity occurred following vaginal delivery (5.3 / 1000 live
births). The amount of neonatal
respiratory morbidity increased following caesarean section during labour (12.2
/ 1000 live births), and further increased following elective caesarean section
(35.5 / 1000 live births). The
audit presented in this paper supports the view that elective caesarean section
is a risk factor for neonatal respiratory morbidity.
There are a number of reasons why caesarean section might increase the
incidence of neonatal respiratory morbidity.
Infants delivered by caesarean section prior to the onset of labour, do
not undergo the same stresses as those infants who are delivered vaginally.
During labour, both maternal and fetal catecholamines are produced in
response to stress and these are necessary to facilitate the clearance of fetal
lung fluid 6. Infants
delivered by caesarean section avoid the opportunity to have lung fluid squeezed
out of their chests as they descend through the birth canal and this will also
predispose these infants to TTN 6.
Furthermore, an inappropriately timed delivery may result in iatrogenic
neonatal respiratory distress syndrome 7, 8.
For singleton pregnancies the lowest risk of neonatal respiratory
morbidity following elective caesarean section is beyond 39 weeks gestation 1.
Morrison et al 1 estimated that by delaying elective delivery
until 39 weeks, neonatal intensive care units in the UK would have a reduction
of greater than one thousand admissions each year.
This has significant financial and social implications, especially as the
rate of caesarean section in Scotland continues to increase9.
The audit presented in this paper also demonstrates that delaying elective
caesarean section until 39 weeks gestation can reduce neonatal respiratory
morbidity. The number of neonates
with respiratory illness following caesarean section fell from 8.8% to 5.5%.
There was also a reduction in the number of infants requiring neonatal
intensive care admission, assisted ventilation and oxygen therapy between the 2
audit cycles. However although a
reduction in neonatal respiratory illness was seen, these findings were not
statistically significant. It is possible that a type-2 statistical error exists and
that the numbers in this audit were too small to demonstrate a statistically
significant difference. A power calculation indicates that more than a thousand
cases would be required in each audit group to confirm that the differences are
statistically significant.
Based on the admission rates seen in the first cycle of the audit, if
there had been no change in practice, one would have expected 29 infants to be
admitted to the neonatal unit with respiratory morbidity (Table
III). Although there was not a
statistically significant reduction in the number of neonatal admissions for
respiratory distress following elective caesarean section, 11 infants were
potentially saved from respiratory illness because of the decision to delay
caesarean section until 39 weeks gestation.
The figures for the rates of neonatal respiratory morbidity following
elective caesarean section at the Glasgow Royal Maternity Hospital compare
favourably to other published figures. Hales et al 10 reported a
frequency of respiratory morbidity of 12.4% following elective caesarean
delivery. Cohen et al 11
described a frequency of respiratory morbidity of 11.2% following elective
caesarean section prior to the onset of labour.
Hack et al 12 reported a figure of 18%, while Parilla et al 13
reported a frequency of 10.1%. Sabrine
14 reported that 2.6% of infants delivered by elective caesarean
section after 37 weeks gestation in a District General Hospital required
neonatal intensive care admission. In the first cycle of the audit 3.4% of
infants delivered by elective caesarean section required admission to the
neonatal intensive care unit. This
fell to 1.5% in the second part of the audit.
In both audit cycles the overall frequency of neonatal respiratory
morbidity following elective caesarean delivery decreased with increasing
gestation. There was also a
significant tendency for infants who were delivered at later gestations to
require less respiratory support. Although
a number of infants still have respiratory illness following elective caesarean
at 39 weeks gestation, it appears to be of a less serious nature. Again this provides further evidence that elective caesarean
sections should be delayed wherever possible until after 39 weeks gestation.
The
conclusion from the first cycle of the audit was to delay elective caesarean
section until 39 weeks gestation unless there was a clear obstetric indication
to deliver earlier. Obstetric staff
were made aware of this recommendation at a department meeting at which the
majority of senior obstetric staff were present. Despite this 84
/ 327 (25.7%) infants were delivered by elective caesarean section before
39 weeks gestation in the second audit cycle.
No other specific action was taken to ensure compliance with this
recommendation and this lack of reinforcement is likely to have contributed to
the number of elective deliveries occurring before 39 weeks gestation in the
second audit cycle.
It was clear that when the first audit cycle was presented that there was
a lack of awareness among some obstetric staff of the findings of Morrison et al1.
This undoubtedly contributed to neonatal respiratory morbidity following
elective caesarean section in the first audit cycle.
During the second audit cycle a number of caesarean sections were being
performed in the days preceding 39 weeks gestation. It is possible that staff at this time believed that they
were close enough to 39 weeks and that it was therefore safe to perform an
elective caesarean section. This
audit has shown that days do make a difference in preventing neonatal
respiratory morbidity and our colleagues are now aware of this.
At
the time that this audit was conducted senior obstetric staff had fixed sessions
on labour ward when they were available for caesarean section.
It is not unreasonable that consultants wish their patients to be
delivered at a time when they were available.
This again may have contributed to those caesarean sections being
performed in the days preceding 39 weeks gestation when consultants may have
felt falsely reassured.
In
the second audit cycle 11 / 84 (13.1%) infants delivered by elective caesarean
section before 39 weeks gestation required admission to the neonatal unit
because of respiratory illness. Could
any of this morbidity have been prevented?
In order to assess this we must examine the indications for caesarean
section in those infants delivered before 39 weeks who suffered respiratory
morbidity.
During
the second audit cycle at 37 weeks gestation 3 infants were admitted to the
neonatal unit with respiratory morbidity following elective caesarean section.
2 twin infants were delivered by caesarean section because twin 1 was a
breech presentation. The other
infant admitted following elective caesarean section at 37 weeks gestation was
delivered because of suspected macrosomia.
Indeed the infant weighed 4.8kg, which is significantly greater than the
95th centile for gestational age.
At
38 weeks gestation 8 infants were admitted to the neonatal unit with respiratory
morbidity following elective caesarean section.
In 4 of these cases the primary indication for caesarean section was
previous caesarean section. In 1 case the indication was for breech presentation.
Of the others 2 mothers had a history of stillbirth in previous
pregnancies and 1 had a history of severe shoulder dystocia with subsequent
infant morbidity.
There
is evidence that delaying elective caesarean section in twins until 38 weeks
gestation can prevent neonatal respiratory morbidity15.
One could therefore argue that in the second audit cycle 2 cases of
neonatal respiratory illness following delivery at 37 weeks gestation could have
been prevented if their delivery had been delayed until 38 weeks gestation.
Of those infants delivered at 38 weeks gestation in the second audit
cycle there are clearly cases that could potentially have been delayed until 39
weeks gestation. It is therefore
possible that an even greater reduction in neonatal respiratory morbidity
following elective caesarean section can be achieved.
Following
completion of the second audit cycle the findings were presented at
departmental, regional and national meetings.
In future greater awareness of the neonatal benefits of delaying elective
caesarean section until 39 weeks gestation could be achieved at a department
level by displaying poster reminders in antenatal clinics and labour ward, and
also in the folder that is used to book elective operative deliveries.
With these changes one would hope that we could further reduce the number
of caesarean sections being performed prematurely before 39 weeks gestation and
thus further reduce neonatal respiratory morbidity.
By
postponing elective caesarean section until 39 weeks gestation, a number of
women will present in spontaneous labour. Morrison
et al 1 reported that caesarean delivery following the onset of
labour reduces the amount of neonatal respiratory morbidity.
However this must be balanced against the potential risks to both the
mother and the fetus, of performing such a delivery outside normal working
hours.
Conclusion:
Neonatal respiratory morbidity following elective caesarean section is a
significant problem, affecting 8.8% of infants born at the Glasgow Royal
Maternity Hospital between October 1996 and October 1997.
Following the first audit this figure fell to 5.5%.
The results of this audit support the view that delaying elective
caesarean section until 39 weeks gestation can prevent neonatal respiratory
morbidity. Further work is required to show that delaying elective
caesarean section until 39 weeks gestation is not associated with an increase in
maternal and neonatal morbidity due to an increase in emergency caesarean
sections.
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