Transcript Isolated single umbilical artery, perinatal outcomein

The use of thromboelastography to assess
haemostatic changes in post-partum women.
HJ MAYBURY, AS GORNALL, *JJ KURINCZUK, JC KONJE, **S PAVORD, JJ WAUGH
Department of Obstetrics and Gynaecology, *Department of Epidemiology and Public
Health, **Department of Haematology, University of Leicester
Introduction
Thromboembolic disease remains the leading cause of maternal mortality in
the UK. Figures from the triennial report of maternal deaths show that 33% of
all direct deaths are due to thromboembolic disease with more than half
occurring in the puerperium1. Furthermore, even treated deep vein thrombosis
is associated with significant morbidity with post thrombotic syndrome
occurring in up to 80% of cases2. Our current belief is that women remain
hypercoagulable for 6 weeks after delivery. This is based on old
epidemiological data from women presenting with thromboembolism in the
post-partum period, there is no scientific evidence to support this.
All pregnant women are rendered hypercoagulable by the marked alteration of
clotting factors. Fibrinogen levels increase by 50% and there are increased
levels of factors VII, VIII and X4. Endogenous anticoagulants decrease during
pregnancy with the development of functional resistance to activated Protein C
in 40% of pregnancies and a fall in Protein S levels5 furthermore, during
delivery endothelial damage occurs which may trigger clot formation. In the
antenatal period the increasing gravid uterus results in raised venous pressure
and venous stasis. The combination of these factors, which fulfil Vichow’s
triad, results in a 10 fold increased risk for venous thrombosis in pregnancy
which increases to 25 fold in the postpartum period.
Fig 2. Traces generated by thromboelastograph, days 1,9,25 and 64
post-partum from the same individual.
Results
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R
Aim
To determine the time course for blood clotting mechanisms to return to prepregnancy levels in low risk women, following a normal vaginal delivery using
thromboelastography.
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Methods
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• 334 citrated blood samples from 71 low risk women were
collected
prospectively
for
10
weeks
after
normal
delivery
and
analysed by thromboelastography after 30 minutes and within 3 hours.
• Single citrated blood samples were collected from non-pregnant
50
female controls
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20
30
40
50
60
70
80
Days
Fig 3. A scattergram of R value of the thromboelastograph vs time in days
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90
80
70
MA
Recruitment Criteria
Subjects
Normal vaginal delivery at term
Total blood loss 400mls
Controls
Non pregnant women
Age <40 years
Uncomplicated pregnancy
No intercurrent illnesses
No chronic illness
No regular medication
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50
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30
20
10
No regular medication Not taking combined oral
No past history of clotting disorders
contraceptive pill
or thromboembolic event.
Technique
Thromboelastography is a tool that enables the global assessment of blood
clotting to be made from a single blood sample2. It detects more subtle
changes compared to conventional changes and provides additional
information about blood clot kinetics.
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80
Days
Fig 4. A scattergram of maximum amplitude (MA) of the thromboelastograph vs time in days
• The mean R value on days 1 and 2 postpartum is 8.4 min
(range 3.5-14.0, SD 2.1) compared with 13.9 min (range
6.0-20.5, SD 3.73) in the non-pregnant controls (p<0.0001)
• The mean MA value on days 1 and 2 postpartum 68.9 mm
(range 58.0-92.0, SD 5.8) compared with 53.7 mm (range
44.0-76.0, SD 7.3) in the non-pregnant controls (p<0.0001)
• The R value in the postpartum group reaches that of the
non-pregnant controls at 25 days
• The MA value in the postpartum group reaches that of the
non-pregnant controls at 32 days.
Conclusion
• Thromboelastography demonstrates that low risk women are
significantly more hypercoagulable after delivery than
nonpregnant controls.
• In low risk women the hypercoagulable state has resolved by
32 days postpartum
R time (reaction time) is the latency time from placing the blood in the cup
until the clot starts to form
K time is arbitrarily assigned as the time between the TEG trace reaching
2mm and going up to 20mm
α angle is the slope drawn from the R to K value
MA (maximum amplitude) is the greatest vertical amplitude of the TEG trace
References
1. The Royal College of Obstetricians and Gynaecologists Study Group in Maternal
Morbidity and Mortality. Edited by Allan B. Maclean and James P. Neilson. RCOG
Press.
2. Mallet SV, Cox DJA. Thromboelastography and sex differences. Br J Anaes
1992;69:307-313.