The use of thromboelastography to assess haemostatic changes in post-partum women.

HJ MAYBURY, AS GORNALL, *JJ KURINCZUK, JC KONJE, **S PAVORD, JJ WAUGHDepartment of Obstetrics and Gynaecology, *Department of Epidemiology and Public Health, **Department of Haematology, University of Leicester

IntroductionThromboembolic 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.

AimTo determine the time course for blood clotting mechanisms to return to pre-pregnancy levels in low risk women, following a normal vaginal delivery using thromboelastography.

Methods• 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

Recruitment CriteriaSubjects ControlsNormal vaginal delivery at term Non pregnant women

Total blood loss 400mls Age <40 years

Uncomplicated pregnancy No chronic illness

No intercurrent illnesses No regular medication

No regular medication Not taking combined oral

No past history of clotting disorders contraceptive pill

or thromboembolic event.

TechniqueThromboelastography 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.

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

Fig 2. Traces generated by thromboelastograph, days 1,9,25 and 64 post-partum from the same individual.

References1. 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.

• 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

Fig 3. A scattergram of R value of the thromboelastograph vs time in days

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

Days

R

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80

Days

MA

Fig 4. A scattergram of maximum amplitude (MA) of the thromboelastograph vs time in days

Results