HPA-1a alloimmunization and pregnancy outcome in a Polish screening program: PREVFNAIT

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) caused by antibodies to human platelet antigen (HPA)-1a in white HPA-1a-negative mothers is the most frequent cause of intracranial hemorrhage (ICH) in otherwise healthy newborns.

To investigate the natural history of FNAIT and establish a biobank from HPA-1a-negative alloimmunized and nonimmunized pregnancies.

A total of 24,259 pregnant women were recruited to the study during 2013-2017 and 24,236 were screened for HPA-1a. Anti-HPA-1a antibodies were tested by Monoclonal Antibody Immobilization of Platelet Antigens (MAIPA) and some samples (MAIPA-negative), with Luminex bead-based immunoassay (PAKLx) if the neonate had thrombocytopenia and/or ICH. HPA-1 genotyping of fathers, fetuses (from maternal plasma), and newborns was performed. Biological material was stored in biobanks in Norway and Poland.

Among 583/24,236 (2.4%) HPA-1a-negative women, samples were obtained from 529, of which 513 were examined during pregnancy. Anti-HPA-1a antibodies were detected in 48/529 (9.1%) women; whereof 34/513 (6.6%) during pregnancy, either by prospective MAIPA (n = 27) or in retrospect by PAKLx in MAIPA-negatives (n = 7). FNAIT was diagnosed in 11/34 (32%) neonates from alloimmunized pregnancies: in 6/11 cases by prospective MAIPA and in 5/11 by retrospective PAKLx. There were no neonates with FNAIT-associated ICH delivered by MAIPA-positive women, but 3 ICH/severe thrombocytopenia cases were diagnosed by PAKLx. Among nonimmunized HPA-1a-negative women, 28 newborns had thrombocytopenia and 2 others had ICH.

Feasibility of HPA-1 antenatal screening was demonstrated, and a comprehensive biobank was established. The FNAIT detection rate was improved by retrospective diagnostics by PAKLx, including 3 newborns with ICH not identified by prospective MAIPA.