FRCA Notes

Thrombocytopaenia in Obstetrics

Resources

  • Thrombocytopaenia, a platelet count of <150x109/L, is the second commonest haematological abnormality in pregnancy, after anaemia
  • It affects between 7-12% of pregnancies and is of interest owing to the ramifications for neuraxial intervention
  • Spinal canal or epidural haematoma is a rare albeit potentially devastating complication; the incidence in those with thrombocytopaenia is unknown

Pregnancy-independent Pregnancy-related
Hereditary/idiopathic thrombocytopaenia Gestational thrombocytopaenia
Immune thrombocytopaenic purpura (ITP) Pre-eclampsia
Heparin-induced HELLP syndrome
Viral-induced DIC
TTP Acute fatty liver of pregnancy

ITP

  • Affects <0.1% of pregnancies
  • An auto-immune, IgG-mediated disease leading to increased platelet splenic sequestration/destruction
    • These antibodies can cross the placenta and cause neonatal thrombocytopaenia
  • Typically causes thrombocytopaenia in the first and second trimesters although can occur at any time
  • There may be symptoms such as minor bruising, petechiae although can be asymptomatic or cause more deleterious bleeding
  • Platelet count usually remains >30x109/L although platelets may be hyper-functional
  • Suggested to avoid ventouse delivery

Gestational thrombocytopaenia

  • Affects 5 - 10% of pregnancies
  • Accounts for 75% of obstetric thrombocytopaenia
  • Arises due to plasma volume expansion in a similar fashion to anaemia of pregnancy; platelet count falls ~17%
  • Onset in the late second or third trimester
  • Typically asymptomatic and spontaneously resolving
  • Platelet count usually remains >70x109/L and neuraxial intervention is rarely contraindicated

Pre-eclampsia and HELLP syndrome

  • These conditions affect 5 - 8% (PET) and <1% (HELLP) of pregnancies
  • They are the second commonest cause of obstetric thrombocytopaenia after gestational thrombocytopaenia
  • Platelet count can drop rapidly so frequent testing is required (see below) to enable timely (neuraxial) intervention

Acute fatty liver in pregnancy

  • Affects <0.01% of pregnancies
  • Onset in the third trimester with acute liver injury/liver failure
  • Platelet count usually remains >50x109/L

  • There is an absence of robust evidence about the levels of platelet count at which it is safe to perform a neuraxial intervention
  • There is equally a lack of evidence surrounding appropriate platelet levels at which one can safely remove indwelling epidural catheters; in general the same criteria as for insertion are followed
  • As ever, there is a balance to be struck between risks (epidural haematoma) and benefits (labour analgesia, avoiding GA)

  • For otherwise healthy individuals, a platelet count >100x109/L is not associated with an increased risk of complications
  • The risk of epidural haematoma increases with falling platelet counts, in one study reported as:
    • 0.2% - platelets 70 - 100x109/L
    • 3% - platelets 50 - 69x109/L
    • 11% - platelets <50x109/L

'Safe' platelet levels

  • A platelet count >70 - 75 x 109/L is generally deemed acceptable for administering regional blockade, provided:
    • There are no other risk factors
    • The platelet count is not falling

  • In patients where there are risk factors e.g. pre-eclampsia:
    • Platelets 75 (or 80) - 100x109/L
      • Check a clotting screen
      • If normal, neuraxial intervention is acceptable
    • Platelets 50 - 75x109/L
      • Neuraxial intervention should only be performed by an experienced obstetric anaesthetist following an appropriate risk-benefit decision
      • The patient should be carefully monitored for signs of an epidural haematoma
      • (There is a case report of epidural haematoma at platelet count of 71 x 109/L)
    • Platelets <50x109/L
      • Generally felt to be an absolute contraindication to both neuraxial intervention and operative delivery
      • The 2013 AAGBI/OAA guideline (link above) comments a "stable level of 40x109/L may be safe for lumbar puncture in the absence of other coagulation abnormalities"

Ante-natal management

  • Patients should be reviewed by the appropriate Obstetric, Midwifery and Anaesthetic stakeholders
  • Local pathways/policies may include Haematology referral or joint clinics
  • Specific management will depend somewhat on the aetiology

  • For ITP:
    • Regular platelet monitoring - up to 30% will require intervention in pregnancy
    • Symptoms (i.e. bleeding) or platelet levels <30x109/L generally require treatment
    • First line is corticosteroids e.g. prednisolone 10-20mg daily
    • In those refractory to steroids or requiring rapid increases, IVIg is used instead
    • Platelet transfusions aren't recommended in isolation as they'll merely be consumed; should be given alongside IVIg or high-dose steroids

Investigations and timing of platelet counts

  • Standard investigations may include:
    • FBC, although this only assesses platelet quantity and not quality
    • Clotting studies, which provide little in the way of qualitatitve or quantitative information about platelets
    • Viscoelastic haemostatic assays (e.g. TEG, ROTEM)
      • Limited correlation between assay results and clinical bleeding in patients except at very low platelet levels
      • Rather limited evidence for using these prior to neuraxial intervention in obstetric patients with thrombocytopaenia
  • More specialised investigations may be performed depending on the aetiology e.g. blood film, platelet aggregation studies

  • In the patient for whom there is no reason to suspect low or falling platelet count, an antenatal FBC beyond 28 weeks with a platelet count >150x109/L is sufficient
  • In patients where there is suspicion of a low or falling platelet count, it should be checked within 6hrs of neuraxial intervention
  • In those with HELLP syndrome, the count should be checked within 2hrs of neuraxial intervention

Methods for raising platelets

  • Treat offending cause e.g. stop heparin injection/infusion, treat cause of DIC, management of pre-eclampsia
  • Steroids ± IVIg in ITP (see above)

  • Desmopressin (ddAVP)
    • E.g. 0.3μg/kg IV over 30mins
    • This vasopressin relative promotes platelet adhesion
    • Use with in PET as it causes ADH secretion and leads to water retention
    • Can increase the rate of thrombus formation

  • Platelet transfusion
    • As with any transfusion this carries its own risks which need to be balanced against the perceived benefits
    • May prove futile in states of increase platelet consumption e.g. ITP and are generally less effective in PET/HELLP
    • Generally reserved for platelet counts <50x109/L