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To cite this article: Bertrand G, Martageix C, Jallu V, Vitry F, Kaplan C. Predictive value of sequential maternal anti-HPA-1a antibody concentrations for the severity of fetal alloimmune thrombocytopenia. J Thromb Haemost 2006; 4: 628-37.Summary. Background: Fetal/neonatal alloimmune thrombocytopenia results from maternal immunization against fetal platelet alloantigens (HPAs), and the major risk is intracranial hemorrhage. The severity of thrombocytopenia increases in subsequent pregnancies, and antenatal therapy has been developed. Until now, the fetal status can only be assessed by fetal blood sampling, which carries a risk of fetal loss or premature delivery. Objectives: To develop non-invasive methods to gain information on the fetal condition. Patients/ methods: Quantification of the maternal anti-HPA-1a alloantibody concentration was performed with a standardized monoclonal antibody-specific immobilization of platelet antigens (MAIPA) procedure for 43 mothers. A correlation between this concentration and the fetal/neonatal platelet counts was studied. Results: (i) Before antenatal therapy, there was a significant correlation between maternal anti-HPA-1a concentrations ‡250 AU mL )1 and fetal thrombocytopenia (2-66 · 10 9 L )1) whatever the gestational age (Fisher's exact test P ¼ 0.0021). (ii) During subsequent pregnancies, we observed a decrease of the maternal anti-HPA-1a concentration for 14/19 women. Just before delivery, all women had anti-HPA-1a concentrations <250 AU mL )1. In four cases, there was a therapy failure and the severely thrombocytopenic babies required postnatal therapy. Conclusion: The maternal anti-HPA-1a concentration could provide obstetricians with clinically useful information concerning the appropriateness and the timing of invasive monitoring procedures. However, though we observed a tendency toward a decrease in maternal antibody concentration after treatment, this finding does not allow us to draw any conclusions on the effectiveness of therapy.

This analysis confirms that anti-HPA-9bw (Max(a)) FMAIT is not uncommon and was found to be approximately 2 percent of our confirmed FMAIT cases. It is a clinically severe syndrome that requires prompt diagnosis, albeit difficult, and maternal PLT transfusion therapy. Laboratory investigation of a suspected FMAIT case should be carried out in a specialist laboratory well-experienced in optimal testing. Appropriate management and antenatal therapy should be considered for successive pregnancies to prevent fetal bleeding.

The frequency of human platelet antigen-1 (HPA-1) to HPA-11w (excluding HPA-8w) and HPA-15 systems was studied in four sub-Saharan populations: Beninese, Congolese (Democratic Republic of Congo Kinshasa), Cameroonians, and Aka pygmies (Central African Republic). No report of HPA prevalence has previously been published concerning these populations which are characterized by the highest HPA-2b gene frequencies of any reported to date (Aka 0.393, Benin 0.292, Cameroon 0.237, and Congo 0.224) and at lesser degree HPA-5b (Aka 0.405, Congo 0.268, Cameroon 0.254, and Benin 0.182). This study is of great importance (i) particularly in the context of the diversity caused by the population migrations, we may observe today in our hospitals (ii) to confirm that the Pygmy population with distinctive frequencies (absence of the HPA-1b, HPA-2b, and HPA-5b highest frequencies) is an isolated population.