Key Points: The systematic review suggests that first-line antenatal management in FNAIT is weekly IVIG administration. Noninvasive management is effective without the relatively high rate of adverse outcomes seen in invasive strategies.

Fetal/neonatal alloimmune thrombocytopenia is the most common cause of severe thrombocytopenia in the fetus and in an otherwise healthy newborn. To counter the consequences of severe fetal thrombocytopenia, antenatal therapies have been implemented. Predictive parameters for fetal severe thrombocytopenia are important for the development of noninvasive strategy and tailored intervention. We report here data concerning 239 pregnancies in 75 HPA-1bb women. Analysis of the index cases (diagnosis of fetal/neonatal alloimmune thrombocytopenia) did not show any significant correlation between the severity of the disease and the maternal genetic background (ABO blood group and HLA-DRB3 allele). Subsequent pregnancies were managed, and therapy effectiveness was evaluated. The highest mean newborn platelet count was observed for a combination of intravenous immunoglobulin and steroids (135 × 10⁹/L; 54 newborns) compared with intravenous immunoglobulin alone (89 × 10⁹/L; 27 newborns). The maternal anti-HPA-1a antibody concentration measured before any treatment and before 28 weeks of gestation was predictive of the fetal status. The weighted areas under curves of the maternal alloantibody concentrations were predictive of therapy response. To conclude, this large retrospective survey gives new insights on maternal predictive parameters for fetal status and therapy effectiveness allowing noninvasive strategies.

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 × 10⁹ L⁻¹) whatever the gestational age (Fisher's exact test P = 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.