Noninvasive Fetal HPA Genotyping for FNAIT: Diagnostic Accuracy and Technical Performance of Molecular Methods

Noninvasive fetal human platelet antigen (HPA) genotyping has emerged as a promising tool for diagnosing fetal and neonatal alloimmune thrombocytopenia (FNAIT). Detection of fetal HPA incompatibility using cell-free fetal DNA from maternal blood allows for early, risk-adapted clinical assessment. This review evaluates the diagnostic accuracy, technical performance, and clinical applicability of noninvasive fetal HPA genotyping methods, including real-time polymerase chain reaction (PCR), allele-specific quantitative PCR, high-resolution melting PCR, droplet digital PCR (ddPCR), and next-generation sequencing (NGS). Across the analyzed studies, conventional PCR-based methods demonstrated reliable diagnostic performance for targeted HPA systems, particularly HPA-1, with consistent results at later gestational ages and suitability for routine molecular diagnostic laboratories. More advanced approaches, such as ddPCR and NGS, enabled accurate, multiplex fetal HPA genotyping across multiple antigen systems, including rarer HPA types, while also exhibiting robust performance at earlier gestational ages and lower fetal DNA fractions. These findings suggest that the choice of method is primarily determined by clinical context, required antigen coverage, and available laboratory infrastructure, with potential implications for risk stratification and clinical decision-making in pregnancies at risk for FNAIT.