CONGRESS 2023 - Acute obstetric coagulopathy

Postpartum haemorrhage is caused by obstetric complications but may be exacerbated by haemostatic impairment. It is a common observation that placental abruption and amniotic fluid embolism are associated with a severe and early coagulopathy characterised by hypofibrinogenaemia and increased fibrinolysis. In Cardiff, a programme of research has been undertaken investigating the early detection and replacement of fibrinogen based on viscoelastic haemostatic assays. This culminated in the development of a care bundle for postpartum haemorrhage called the Obstetric Bleeding Strategy for Wales (OBS Cymru). Introduction of the OBS Cymru intervention across Wales resulted in fewer women experiencing massive postpartum haemorrhage (defined as >2500 mL) and decreased need for blood transfusion. The intervention is being investigated further in a NIHR supported study. At term, women have increased levels of procoagulant clotting factors and reduced anticoagulants leading to a prothrombotic state. Our study confirmed these findings and demonstrated significantly raised thrombin generation. We identified two main types of coagulopathy; a dilutional coagulopathy with coagulation factors and platelets falling progressively with bleed size. However, clinically significant reductions in clotting factors were not seen until bleeds of 3000-4000 mL had occurred due to the high starting levels. Despite this, thrombin generation did not decrease due to increased levels of factor VIII during bleeds. Similar dilution-related falls were seen with fibrinogen levels. The exception was factor XIII which falls at term and decreases further with bleed size. The clinical significance of this finding has not been investigated but could suggest a role for cryoprecipitate. In a subgroup of women we identified an early and severe consumptive coagulopathy caused by hyperfibrinolysis with very high D-dimer and plasmin/antiplasmin complexes which we termed acute obstetric coagulopathy (AOC). In addition, women with AOC had low levels of fibrinogen and evidence of an acquired dysfibrinogenaemia demonstrated by a reduced Clauss/antigenic ratio. The coagulopathy caused depletion of factor V and factor VIII but other clotting factors and thrombin generation was preserved. An increase in activated protein C was observed but no increase in soluble thrombomodulin demonstrating similarities and differences to trauma-induced coagulopathy. AOC occurred in about 1/1000 deliveries and was associated with a high rate of fetal and neonatal deaths. It was most commonly associated with placental abruption but occurred with all underlying causes of postpartum haemorrhage.

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