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ORIGINAL ARTICLE
Estimation of blood loss after cesarean section and vaginal delivery haslow validity with a tendency to exaggeration
CHRISTINA LARSSON1, SISSEL SALTVEDT2, INGELA WIKLUND1, SARA PAHLEN3 &
ELLIKA ANDOLF1
1Division of Obstetrics and Gynecology, Karolinska Institutet, Danderyd Hospital, SE-182 88 Stockholm, Sweden,2Stockholm South General Hospital, Sweden, and 3University of Linkoping, Sweden
AbstractBackground . Excessive bleeding is one of the major threats to women at childbirth. The aim of this study was to validateestimation of blood loss during delivery. Methods . Bleeding was estimated after 29 elective cesarean sections and 26 vaginaldeliveries and compared to blood loss measured by extraction of hemoglobin using the alkaline hematin method, accordingto Newton. Results . Inter-individual agreement of estimation showed good results. Estimated loss in comparison withmeasured loss resulted in an over-estimation. In vaginally delivered women, there was no correlation between estimated andmeasured blood loss (r2�/0.13), and in women delivered by elective cesarean section, the correlation was moderate (r2�/
0.55). Agreement, according to Bland and Altman, indicated that measured blood loss could vary from 570 ml less to342 ml more than estimated blood loss. Conclusions . The standard procedure of estimation of obstetric bleeding was foundto be unreliable. In this study, blood loss was over-estimated in cesareans. In vaginal deliveries, there seemed to be nocorrelation. Estimated blood loss as a quality indicator or as a variable in studies comparing complications must be used withcaution. For clinical purposes, estimation of blood loss and measurement of post partum hemoglobin is of low value andmay lead to the wrong conclusions.
Key words: Blood loss, post partum hemorrhage, comparative study, B-hemoglobin, reproducibility of results, delivery
Introduction
Excessive bleeding after delivery is one of the top five
causes of maternal mortality in developed and
developing countries. Although pregnancy leads to
an increase of the blood volume by roughly 1 l,
control of hemorrhage is necessary. Bleeding from
lacerations or an atonic uterus may be profuse and
amount to a few liters within minutes. This can lead
to life-threatening situations, such as disseminated
intravascular coagulation.
Anemia increases the risk of infection and inter-
feres with recovery after delivery (1). It may, there-
fore, impair early infant contact during this
important period (2).
Blood loss may be estimated in different ways. The
content of drainage bottles can be measured. Swabs,
pads and diapers can be weighed. In most deliveries,
both vaginal and caesarean sections, blood loss is
also estimated visually.
Estimation of blood loss in surgery corresponds
reasonably well to the actual amount according to
some studies (3), but less well according to other
(4,5).
After vaginal delivery, visual estimation is the
predominant method. In obstetrics, the estimation
is impaired by the amount of amniotic fluid and
blood from the placenta.
Few recent studies have evaluated the accuracy of
estimation of blood loss in obstetrics. Estimation
correlated relatively well with small bleedings but not
with large (6). Bleeding was usually underestimated
after vaginal delivery (7�9).
Massive hemorrhage was only noticed if blood
pressure and pulse were affected (10).
Correspondence: C. Larsson MD, Division of Obstetrics and Gynecology, Karolinska Institutet, Danderyd Hospital, SE-182 88 Stockholm, Sweden. E-mail:
Acta Obstetricia et Gynecologica. 2006; 85: 1448�1452
(Received 24 August 2006; accepted 25 August 2006)
ISSN 0001-6349 print/ISSN 1600-0412 online # 2006 Taylor & Francis
DOI: 10.1080/00016340600985032
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Studies of the estimation of hemorrhage after
cesarean section are few (11,12), and not relevant
due to the change in anesthesiologist and surgical
techniques during recent years (13). No study has
compared the validity of estimation of blood loss in
different modes of delivery, which is of interest when
comparing complications.
The aim of this study was to validate estimation of
blood loss after vaginal delivery and elective cesarean
section, and to investigate if post partum hemoglo-
bin reflects blood loss.
Material and methods
Women undergoing elective or semi-acute cesarean
section or vaginal delivery were included. As the
obstetric procedure was not to be studied, but rather
the assessment of blood loss, both primiparas and
multiparas were included. All cesareans were per-
formed under spinal anesthesia. After cesarean
delivery, blood loss was estimated by the obstetrician
and the anesthetic nurse together. The content of
drainage bottles was measured and added. After
vaginal delivery, the blood loss was visually estimated
by the midwife according to the routine of the
hospital. When there were difficulties in estimating
the blood loss or when the loss visually exceeded
500 ml, pads, swabs and diapers were weighed.
These estimations represent standard procedure.
Initially, to compare inter-individual variation of
estimation of blood loss, two skilled midwives
estimated the blood loss in 10 vaginal deliveries
independent of one another. Blood loss was also
estimated in 16 cesarean sections simultaneously by
2 persons, independent of one another (the obste-
trician and anesthetic nurse on duty).
To study the validity of estimation, estimated
blood loss was compared to the measured amount.
For this purpose, results from another 29 women
delivered by cesarean section (s) and 26 women
delivered vaginally (v) were analysed. Estimation of
blood was performed as described above. Measure-
ment of blood loss was performed using the alkaline
hematin method (14). All the blood-stained pads,
diapers and swabs and the content in the drainage
bottle were collected, put in a plastic bag and
blended with 5% NaOH solution. The plastic bag
was then transferred to the Stomacher Lab Blender
(Model 3500, Seward Laboratories, London, UK)
and processed for a few minutes. In this way, the
hemoglobin was extracted. A portion of the fluid was
collected and diluted with 5% NaOH solution. The
concentration of alkaline hematin was obtained by
assay in a spectrophotometer at 546 nm with the
appropriate NaOH as a blank. The intra-assay
coefficient for analysing the concentration is 1%.
The blood loss was then calculated using the
patient’s hemoglobin at admittance as a reference.
On admittance, as well as 3�7 days postpartum, the
level of hemoglobin in the blood was analysed in all
participants.
The study was approved by the local Medical
Ethics Committee and the subjects gave their
informed consent.
Statistical methods
Intra-class correlation coefficient [ICC] was calcu-
lated with the SSPS program to assess the inter-
observer repeatability (15).
All other statistical analyses of the data were
performed using JMP statistical package (SAS In-
stitute Inc., JMP Sales, SAS Campus Drive, Cary,
NC 27513, USA).
Blood loss was not normally distributed and,
therefore, the Wilcoxon two-sample test was used.
The co-variation between variables was assessed by
bivariate linear regression. Agreement between
methods was analysed according to Bland and Alt-
man (16).
Results
When the blood loss was estimated simultaneously
by two persons, the ICC was 0.92 (95% CI 0.70�0.98) in vaginal deliveries and 0.97 (95% CI 0.91�0.99) in cesarean sections. Both correlations are
significant with p-values B/0.001.
As for the comparison of estimated and measured
blood loss, results from another 29 women delivered
by cesarean section (s) and 26 women delivered
vaginally (v) were analysed. In all, 20 midwives were
involved in the vaginal deliveries and 7 obstetricians
in estimating the blood loss of the cesarean sections.
Women in this latter part of the study delivered by
cesarean section were older, 34 years (CI 95% 32.3�35.1) versus 30 years (CI 95% 28.9�31.8), and
gestational age was shorter, 270 days (CI 95% 269�275) versus 281 days (CI 95% 278�284). As
expected, the gestational age was skewed to the left
in women who delivered by elective cesarean section
as opposed to those who delivered vaginally. Parity
did not differ: there were 12 primiparas out of 29 (s)
versus 17 out of 26 (v).
The median blood loss in the vaginal group was
325 ml (200�1300 ml) according to estimation and
254 ml (102�715) according to the hemoglobin
extraction method (p�/0.07). The median blood
loss in the cesarean group was 500 ml (200�1500 ml) according to estimation and 440 ml
Estimation of blood loss in delivery 1449
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(135�1000) according to the hemoglobin extraction
method (p�/0.1). Estimated blood loss for the whole
group (n�/55) was 400 ml compared to the mea-
sured loss of 370 ml (p�/0.05) (Figure 1). Regres-
sion showed a moderate correlation (r2�/0.55)
between estimated and measured blood loss in the
(s) group (Figure 2). In the (v) group (r2�/0.13),
there was no correlation (Figure 3). Plotting the
difference between estimated and measured blood
loss against measured blood loss, there was no
correlation (r2�/0.001) (Figure 4).
Agreement between the methods, according to
Bland and Altman (16), showed that estimation
tended to over-estimate the bleeding by a mean of
114 ml (SD 228). This indicates that the true result
of measured blood loss could be between �/570 (�/2
SD) and �/342 (�/2 SD) ml from the estimated
(Figure 5). For vaginally delivered only, mean would
be �/101 (SD 240) indicating a range from �/581
to �/379. For women delivered by cesarean section,
a mean of�/26 (SD 220) indicating a range of �/566
to �/314.
The decline of hemoglobin (difference between
hemoglobin analysed at admittance to the delivery
ward and hemoglobin 3�7 days post partum) did not
correlate to the result of blood loss (r2�/0.05). Only
17 patients were available for this analysis.
Discussion
The alkaline hematin method has been used in
other studies (3). The Stomacher Lab-Blender
simplifies the procedure and measurements of
known volumes of blood in pads have been excellent
Blo
od lo
ss
0
200
400
600
800
1000
1200
1400
1600
Estimated MeasuredMethod
Figure 1. Estimated and measured blood loss in women delivered
by cesarean section and vaginal delivery. Values are given as
median and percentiles with the ends of the box as the 25th and
75th percentiles and the 10th and 90th percentiles indicated.
0
500
1000
1500
Est
imat
ed
100 200 300 400 500 600 700 800 900 1000Measured
Figure 2. Estimated and measured blood loss in women delivered
by cesarean section. Estimated blood loss is plotted as the
dependent variable and measured as the independent.
0
200
400
600
800
1000
1200
1400
Est
imat
ed
100 200 300 400 500 600 700 800
Measured
Figure 3. Estimated and measured blood loss in women delivered
vaginally.
-400
-200
0
200
400
600
800
1000
Est
imat
ed-m
easu
red
100 200 300 400 500 600 700 800 900 1000Measured
Figure 4. There was no correlation between the difference of
estimated and measured blood loss and measured.
1450 C. Larsson et al.
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(14). The measured amount in our study is,
therefore, considered to be ‘the true amount’. Errors
can occur if all pads are not collected. Since
estimation was performed on the same occasion as
measurement, this was less likely to occur.
There was good agreement between estimations
performed by different persons in the same hospital.
Since estimation of blood loss is routine in our
hospital, there are guidelines to assist the staff even if
no written instructions are at hand.
On the other hand, estimation in comparison with
measured blood loss resulted in an over-estimation
of blood loss in our study. This indicates that clinical
routine has to be checked with objective methods. In
women delivered by cesarean section, measured
blood loss correlated better with estimated loss
than in women delivered by vaginal delivery, where
there was no correlation. In the first case, blood loss
was estimated by the obstetrician and the anesthetist
nurse, and in the latter, by the midwife. Anesthetic
nurses, who are used to various surgical procedures,
may be more precise in their estimation, while
midwives may be biased, expecting the blood loss
to vary less in normal deliveries.
The interpretation of correlation coefficients when
comparing two methods is difficult. Therefore, a
method recommended by Bland and Altman was
also used, showing estimation to be inaccurate both
in the cesarean and the vaginal group. Other studies
have shown an over-estimation in small bleedings
and an under-estimation in larger bleedings (10), or
an under-estimation when compared to measured
(8,12). The conclusion of these three studies is that
estimation of blood is grossly inaccurate. This
indicates that our findings are generally applicable.
Routines on how to estimate blood loss may also
differ from hospital to hospital and even between
different professions. This indicates that how esti-
mation is carried out may vary in different hands and
locations. Using estimated blood loss as a variable in
quality assurance may therefore be problematic.
Likewise, comparisons of studies should be per-
formed with caution.
Bleedings over 1000 ml were few in this small
study. The alkaline hematin method is also less
suitable for excessive bleedings. Previous studies
have shown that large bleedings are detected only if
blood pressure and pulse are affected (6,10).
No correlation could be seen between measured
blood loss and decline of hemoglobin. Only a
few patients were available for the analysis, but
this agrees with a previous study, where post partum
hemoglobin of almost 700 patients were compared
with estimated blood loss during delivery (17).
After delivery, changes in body fluids occur
which may partly explain this lack of correlation.
Post partum hemoglobin, therefore, seems to be of
limited value.
In summary, estimation of blood loss in associa-
tion with either vaginal delivery or cesarean section is
imprecise, and attention should be paid to this fact in
the clinical situation. Vigilance in monitoring blood
loss after delivery is, however, mandatory. Estima-
tion is the only simple method available, but its
inaccuracy must be kept in mind.
Acknowledgements
The study was supported by Praktikertjanst AB,
Stockholm, Sweden.
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