How does maternal thrombocytopenia (low platelet count) affect babies?

Maternal Thrombocytopenia's Effects on Babies

Maternal thrombocytopenia can cause neonatal thrombocytopenia in 8.9-14.7% of cases, with a very low risk (0-1.5%) of intracranial hemorrhage in affected neonates. 1

Incidence and Risk Assessment

• Neonatal thrombocytopenia due to maternal immune thrombocytopenia (ITP) accounts for only 3% of all cases of thrombocytopenia at delivery 1
• Risk of neonatal thrombocytopenia increases with severity of maternal thrombocytopenia:
  • 0.11% with mild maternal thrombocytopenia (100-149 K/μL)
  • 1.43% with moderate maternal thrombocytopenia (50-99 K/μL)
  • 18.18% with severe maternal thrombocytopenia (<50 K/μL) 2
• Despite this correlation, the overall relationship between maternal and neonatal platelet counts is weak (Pearson r = 0.038) 2

Predictive Factors and Monitoring

• Fetal or neonatal platelet count cannot be reliably predicted by:
  • Maternal platelet count
  • Platelet antibody levels
  • History of maternal splenectomy 1
• Attempts to measure fetal platelet count before delivery are not recommended due to:
  • Fetal blood sampling by cordocentesis carries 1-2% fetal mortality risk
  • Scalp blood sampling is technically difficult and often produces misleading results 1

Management During Delivery

• Mode of delivery should be determined by obstetric indications, not maternal thrombocytopenia status 1
• Procedures with increased hemorrhagic risk should be avoided:
  • Fetal scalp electrodes
  • Fetal blood samples
  • Ventouse delivery
  • Rotational forceps 1

Neonatal Management

• After delivery, obtain cord blood platelet count by clean venepuncture of a cord vessel 1
• Avoid intramuscular injections (including vitamin K) until platelet count is known
• Monitor infants with subnormal counts closely as platelet counts typically nadir between days 2-5 after birth 1
• Perform transcranial ultrasonography on neonates with platelet counts <50 × 10⁹/L 1
• Treatment is rarely required, but consider:
  • For clinical hemorrhage or platelet counts <20 × 10⁹/L: single dose of IVIg 1 g/kg
  • For life-threatening hemorrhage: platelet transfusion combined with IVIg 1

Long-term Considerations

• Neonatal thrombocytopenia secondary to maternal ITP may last for months and requires long-term monitoring 1
• Some infants may need a second dose of IVIg 4-6 weeks after birth 1
• In subsequent pregnancies, the second fetus is usually affected similarly to the first 1

Important Distinctions

• It's crucial to differentiate between neonatal thrombocytopenia due to maternal ITP and neonatal alloimmune thrombocytopenia (NAIT) 1, 3
• NAIT is defined as platelet count <100 × 10⁹/L at birth or within 7 days, or fetal intracranial hemorrhage, without alternative causes 3
• NAIT results from maternal immunization against fetal platelet antigens, while maternal ITP involves autoantibodies 3
• NAIT tends to worsen in subsequent pregnancies, unlike maternal ITP 1

Clinical Pitfalls to Avoid

• Don't assume cesarean section is safer for the thrombocytopenic fetus - there's no evidence supporting this 1
• Don't rely on maternal platelet count alone to predict neonatal thrombocytopenia 1, 2
• Don't perform invasive fetal platelet count measurements before delivery due to high risk 1
• Remember that most hemorrhagic events occur 24-48 hours after delivery at the platelet count nadir, not during delivery 1