Early antenatal screening linked to fetal and neonatal alloimmune thrombocytopenia (FNAIT) shows that this rare immune condition can be detected more effectively when newer antibody tests are used, helping explain why some newborn brain bleeds still occur despite standard testing, according to a study published recently in Transfusion.
In this large population study in Poland, researchers followed 24,236 pregnant women between 2013 and 2017 to understand how often FNAIT developed and how it can be detected earlier. Of these women, 583 (2.4%) were HPA-1a negative, meaning they were at risk of becoming immunized if carrying an HPA-1a–positive fetus.
“An important achievement of our project was the establishment of biobanks with serial samples from immunized and nonimmunized HPA-1a negative pregnancies, including paternal and neonatal samples and placental biopsies which were used and will be used for future studies of FNAIT,” noted the authors of this study.
Read more about testing and diagnosis for FNAIT
Blood samples were available from 529 women and 513 were tested during pregnancy. Antibodies were first measured using the standard MAIPA test, with additional testing using a more sensitive Luminex-based assay called PAKLx when newborns showed low platelets or bleeding.
Anti-HPA-1a antibodies were found in 48 of 529 women (9.1%). During pregnancy, 34 of 513 women (6.6%) had detectable antibodies. FNAIT was diagnosed in 11 of these 34 pregnancies (32%). Importantly, no cases of brain bleeding were found among babies of mothers who tested positive by MAIPA alone. However, three newborns with severe thrombocytopenia and intracranial hemorrhage were identified only through retrospective PAKLx testing, meaning they were missed by standard screening.
Among mothers without detectable antibodies, most babies were healthy, but 28 newborns still had low platelet counts and two had intracranial hemorrhage despite normal platelet levels. Overall, babies born to untreated immunized mothers had significantly lower platelet counts than those from nonimmunized pregnancies. Some women received IVIg treatment, yet FNAIT still occurred in two treated pregnancies.
Genetic factors helped clarify risk. Nearly all immunized women carried babies genetically incompatible for HPA-1a, and the HLA-DRB3*01:01 gene strongly predicted who would form antibodies. Noninvasive fetal testing accurately determined fetal platelet type in nearly all cases tested.
For patients and families, these findings matter because they show that FNAIT can hide during pregnancy if only standard tests are used. Adding more sensitive antibody testing and genetic screening could identify high-risk pregnancies earlier, guide monitoring, and prevent severe bleeding in newborns, especially in future pregnancies after antibodies first appear.
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