Thrombocytopenia in pregnancy

Definition

• Low platelet count in pregnancy, generally considered to be less than 100

Pathophysiology

• Most commonly, thrombocytopenia of pregnancy is caused by dilution from increased plasma volume, similar to anemia in pregnancy, and is usually more noticeable in T2 and T3

Etiology

• Gestational thrombocytopenia of pregnancy (70%)
• Hypertensive disorders (20%)
  • Preeclampsia
  • HELLP
• Immune disorders (5%)
  • Immune-mediated thrombocytopenia (ITP)
  • CAPS
  • SLE
  • Thrombotic microangiopathy: aHUS/TTP
• Other (5%)
  • AFLP

Epidemiology

• About 10% of pregnant women have platelets less than 150

Investigations

• CBC and blood film
  • Look for bicytopenia concerning for thrombotic microangiopathy
  • Platelets <70 more consistent with ITP than gestational thrombocytopenia
• For ITP
  • HIV, HBV, HCV
  • Liver and thyroid tests
  • Immunoglobulin levels
  • DAT
  • APLA and ANA
• Platelet antibody testing is useless

Common Causes

Disease	%	Diagnostic Features	Lab Findings	Clinical Features	Pathophys	Comments
Gestational thrombocytopenia	5-9	Onset 2nd-3rd trimester. Normal PLT previously. No neonatal thrombocytopenia.	Plt >70	Typically normal	Unclear	Diagnosis of exclusion. Resolves postpartum. No fetal thrombocytopenia.
ITP	<1	Onset any trimester. May see thrombocytopenia outside pregnancy.	Plt <100 +/- large platelets	May have bleeding, bruising, petechiae	Antibody-mediated peripheral plt destruction with decrease thrombopoiesis.	Diagnosis of exclusion. May be associated with fetal thrombocytopenia.
Preeclampsia	5-8	Onset late 2nd or 3rd trimester (>20 weeks).	Proteinuria >0.3 g/d	BP ≥140/90	Systemic endothelial dysfunction. Inadequate placentation.	May precede other manifestations of preeclampsia. Can present postpartum.
HELLP	<1	70% late 2nd or 3rd trimester, 30% postpartum.	MAHA, high liver enzymes, high LDH.	Signs of preeclampsia, but may be normotensive without proteinuria.	Same as preeclampsia.	Variant of preeclampsia.
AFLP	<0.01	Onset in 3rd trimester.	Plt >50. High liver panel, creat, WBC, urate, ammonia. High PT/PTT, decreased fibrinogen. Hypoglycemia.	RUQ pain. Jaundice, nausea/vomiting. Hepatic encephalopathy.	Preeclampsia spectrum.	MAHA not characteristic. Conjugated bili often high. Liver dysfunction greater than HELLP/preeclampsia.
TTP/aHUS	<0.01	Onset any trimester, but more common during 3rd or postpartum.	MAHA, elevated creatinine, schostocytes on blood film.	Fever, abdo pain, n/v, headache, vis changes, altered mental status.	Congenital deficiency of ADAMTS13 (TTP) or complement dysregulation (aHUS).	ADAMTS13 activity <5% in TTP. Liver panel and BP usually normal.

Management

• Depends on etiology
• Gestational thrombocytopenia
  • No specific management
• ITP
  • No need to treat until 36 weeks if platelets over 30
  • If platelets < 30 or bleeding
    • Prednisone 0.25-1mg/kg) or IVIg (1g/kg ideally body weight, max 60mg)
  • Monitor newborn for post-partum thrombocytopenia

Prognosis

• In ITP, 25% of neonates will have thrombocytopenia and 10% will need treatment