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Neonatal alloimmune thrombocytopenia: Parental evaluation and pregnancy management

Michael J Paidas, MD
Section Editor
Louise Wilkins-Haug, MD, PhD
Deputy Editor
Vanessa A Barss, MD, FACOG


Neonatal alloimmune thrombocytopenia (NAIT) is a disorder in which fetal platelets contain an antigen inherited from the father that the mother lacks, most commonly human platelet antigen (HPA)-1a incompatibility. The mother then develops antibodies against this paternal antigen and these antibodies cross the placenta and bind to the fetal platelets. Clearance of the antibody-coated platelets results in fetal/neonatal thrombocytopenia; platelet function remains relatively normal. In contrast to Rh(D) alloimmunization, NAIT often affects a first pregnancy [1].

Two plausible mechanisms have been proposed to explain the occurrence of maternal alloimmunization in NAIT. One mechanism involves maternal exposure to HPA on fetal platelets due to fetomaternal bleeding related to obstetrical complications, trauma, or delivery. The other mechanism is maternal exposure to integrin beta-3 on placental syncytiotrophoblast cells during pregnancy [2].

This topic will provide a brief overview of NAIT and discuss parental evaluation and management of affected pregnancies. Postnatal issues are reviewed separately. (See "Causes of neonatal thrombocytopenia", section on 'Fetal and neonatal alloimmune thrombocytopenia'.)


All of the following criteria are necessary to diagnosis neonatal alloimmune thrombocytopenia:

Fetal or neonatal thrombocytopenia

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Literature review current through: Nov 2017. | This topic last updated: Mar 17, 2017.
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