Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused when a pregnant person’s immune system makes antibodies against a baby’s platelets, and results of a a study published recently in Haematologica indicated that subtle differences in those antibodies may help explain why only some pregnancies develop serious complications.
FNAIT is closely related to immune reactions seen in other pregnancy conditions, but it is distinct in that platelet-targeting antibodies can lead to dangerously low platelet counts before or just after birth.
In FNAIT, maternal antibodies most often target the HPA-1a antigen inherited from the father. These antibodies can destroy fetal platelets, raising the risk of bleeding. The most feared complication is bleeding in the brain, called intracranial hemorrhage, which is a major cause of death and long-term disability in affected infants. Doctors currently rely mainly on antibody levels to estimate risk, even though high levels do not always lead to severe disease and low levels do not guarantee safety.
“[O]ur data supports the idea that, besides antibody quantity, qualitative characteristics, such as the fucosylation status, are also likely important determinants in predicting disease severity,” explained the authors of this research.
Read more about the prognosis of FNAIT
Researchers focused on this feature of antibodies called fucosylation, a chemical modification that changes how strongly antibodies activate immune cells. Most antibodies in the blood are about 96% fucosylated, but anti–HPA-1a antibodies in FNAIT vary widely, ranging from about 10% to 95%. Lower fucosylation has previously been linked to more severe FNAIT, suggesting stronger immune destruction of platelets.
To better understand this relationship, investigators analyzed samples from the Dutch HPA screening in pregnancy study, which followed pregnant women with no prior history of FNAIT. This prospective design allowed comparison with earlier studies that mostly included severe cases identified after problems occurred. Among 79 pregnancies, only one severe FNAIT case with fatal brain bleeding was observed, while most were symptom-free or had mild skin or airway bleeding.
The severe case stood out by having both higher antibody levels and lower fucosylation compared with unaffected pregnancies. Across the group, antibody levels alone differed more clearly than fucosylation, but trends suggested that repeated pregnancies and prior miscarriage may influence how aggressive the antibody response becomes. Miscarriage has previously been linked to higher risk of immune sensitization and severe FNAIT.
For patients and families, these findings do not change current care yet, but they offer hope. They suggest that future testing could combine antibody levels with antibody quality to better predict which pregnancies face real danger from FNAIT. Over time, this could mean earlier identification, closer monitoring and safer outcomes for babies at risk of FNAIT.
Sign up here to get the latest news, perspectives, and information about FNAIT sent directly to your inbox. Registration is free and only takes a minute.
