Definition And Baseline Values

• Thrombocytopenia in neonates is defined as a platelet count less than 150,000 per cubic millimeter.
• The mean platelet count is greater than or equal to 200,000 per cubic millimeter in most preterm infants.
• The fifth centile may be as low as 104,000 per cubic millimeter for neonates born at 32 weeks of gestation or less.
• The fifth centile is 123,000 per cubic millimeter for late preterm and term neonates.
• Regardless of gestation, a platelet count of less than 100,000 per cubic millimeter mandates a thorough clinical evaluation.

Etiological Classification

• Disorders of primary hemostasis are predominantly caused by abnormalities in the number or function of platelets.
• The causes of low platelets are broadly classified into increased destruction and decreased production.

Increased Destruction Of Platelets

Decreased Production Of Platelets

Platelet Function Disorders

• Adhesion defects: Bernard-Soulier syndrome, von Willebrand disease.
• Aggregation defects: Glanzmann's thrombasthenia.
• Cytoskeleton defects: Wiskott-Aldrich syndrome, MYH9-related disorders.

Clinical Presentation

• Neonates with platelet disorders typically present with petechiae, small mucosal bleeds, and ecchymosis.
• Immune thrombocytopenia can manifest with mild bleeding that resolves within a week.
• Severe cases can present with intracranial hemorrhage (ICH) leading to death or severe neurodevelopmental sequelae.
• Untreated immune cases have a 10% to 20% risk of developing ICH.

Fetal And Neonatal Alloimmune Thrombocytopenia (FNAIT)

• FNAIT is the most common cause of severe, life-threatening thrombocytopenia in neonates.
• The mother lacks a specific human platelet antigen (commonly HPA 1a or HPA 5b) that the fetus possesses.
• Maternal antibodies cross the placenta and destroy the fetal platelets.
• The mother is completely asymptomatic and has a normal platelet count.
• The clinical presentation in the neonate is highly variable.
• It ranges from asymptomatic thrombocytopenia to major organ bleeds, transient hematuria, bloody stools, and ICH.

Diagnostic Approach

First-Line Investigations

• A complete blood count with a platelet count is the primary investigation.
• A peripheral blood smear is crucial to evaluate the differential diagnosis.
• In a peripheral smear, 1 platelet per oil immersion field corresponds to a count of 10,000 to 15,000 per cubic millimeter.
• Giant platelets on the smear indicate hyperutilization or increased destruction.
• Fragmented red blood cells or schistocytes (greater than 10%) strongly suggest DIC.
• Prothrombin time, activated partial thromboplastin time, and fibrinogen levels should be checked to rule out consumptive coagulopathies like DIC.

Specific Diagnostic Tests

• Human Platelet Antigen (HPA) Analysis: This is indicated if FNAIT is suspected. It tests for the presence of maternal antiplatelet antibodies directed against fetal antigens.
• Cranial Ultrasound: An urgent cranial ultrasound is mandatory to rule out intracranial bleeding in any neonate with a platelet count less than 50,000 per cubic millimeter.

Management Strategies

Platelet Transfusion Guidelines

• Platelet transfusions are indicated based on strict threshold guidelines and the clinical condition of the neonate.
• Random donor platelets are typically used; single donor platelets are reserved for expected prolonged severe thrombocytopenia.
• High-risk neonates have favorable outcomes when restrictive thresholds are utilized.

Transfusion Administration And Practical Tips

• The recommended volume for a platelet transfusion is 10 to 20 mL/kg.
• The recommended rate of administration is 10 to 20 mL/kg/hour.
• A 10 mL/kg dose can increase the platelet count by approximately 100,000 per liter.
• Platelet components must be irradiated and leuko-reduced to prevent transfusion-associated graft-versus-host disease and cytomegalovirus transmission.
• Group O platelets should be avoided for non-O patients whenever possible.

Management Of Fetal And Neonatal Alloimmune Thrombocytopenia (FNAIT)

• Washed maternal platelets or platelets from an antigen-negative donor are the ideal treatment.
• If antigen-negative platelets are unavailable, random donor platelets must be transfused immediately in emergencies.
• Intravenous immunoglobulin (IVIG) is administered concurrently at a dose of 1 g/kg/day for 2 days.
• If the platelet count is less than 25,000 per cubic millimeter, use random donor platelets and IVIG.
• If the platelet count is between 25,000 and 50,000 per cubic millimeter, IVIG alone is indicated.
• In neonates with active bleeding or ICH, the target platelet count must be kept at 100,000 per cubic millimeter.
• Following stabilization, the count should be maintained at 50,000 per cubic millimeter for 7 days.

Management Of Autoimmune Thrombocytopenia (Maternal ITP)

• Perform a platelet count on day one from the cord blood.
• If the count is normal, repeat it on day three.
• If the count is between 100,000 and 150,000 per cubic millimeter, repeat it between days 3 and 5 of life.
• If the count drops below 100,000 per cubic millimeter, monitor daily.
• Unlike FNAIT, random donor platelets are rapidly destroyed by circulating maternal antibodies.
• Platelet transfusions serve only as a temporary measure in autoimmune etiologies.
• IVIG remains the definitive treatment of choice and rapidly raises the platelet count.