Chapter 37. Hematology

Definition

• Antibody made against maternal platelet antigen; antigen is also found on fetal platelets

• Antibody made against paternal platelet antigen; antigen is also found on fetal platelets

Clinical findings

• Mild to moderate thrombocytopenia (20,000–50,000/mm3)
• Petechiae and bruising are common
• Mother usually has thrombocytopenia or history of ITP
• Maternal platelets may be normal because she may have adequate production of platelets to compensate for increased destruction

• May lead to severe thrombocytopenia (<20,000/mm3) and in utero hemorrhagic complications (∼20% of infants with NAIT have intracranial hemorrhages)
• Infant appears healthy but may have petechiae and bruising
• Maternal platelet count is usually normal
• Most common antigen is HPA-1

Pathophysiology

• Maternal autoantibodies cross the placenta and bind to neonatal platelets, causing increased destruction

• Maternal alloantibodies cross the placenta and bind to neonatal platelets, causing increased destruction

Diagnosis

• Identification of autoantibody in maternal serum against antigens on her own platelets

• Identification of alloantibody using paternal platelets and maternal serum

Prenatal management

• Use of steroids to prevent fetal thrombocytopenia is controversial; not shown to be of benefit
• Use of immune globulin to prevent fetal thrombocytopenia is controversial; not shown to be of benefit
• PUBS (Percutaneous Umbilical cord Blood Sampling) seems to be safe but is invasive, and its use is controversial; not shown to be of benefit
• Mode of delivery (cesarean section vs vaginal) does not change maternal or fetal outcomes; cesarean section is not shown to be of benefit

• Use of steroids, immune globulin, PUBS, fetal scalp platelet counts during labor, and elective cesarean delivery can be used on a case-by-case basis

Postnatal management

• May include platelet transfusions (pooled donor), steroids, immune globulin or exchange transfusion
• Transfuse platelets for levels <20,000/mm3 or for clinical bleeding

• If diagnosis is made before delivery, maternal platelets are collected 24 h before delivery
• If infant requires platelet transfusions postnatally, use collected maternal platelets that have been washed and resuspended in plasma

If emergent transfusion is required and maternal platelets are not available, either maternal whole blood or HPA-1–negative donor platelets may be used

Immune globulin at a dose of 1–2 g/kg total given over 2–3 h for 2–5 d has been reported with some success

Steroids can be considered for persistent thrombocytopenia

Platelet ...