Clinical Predictors of Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT)

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare, life-threatening condition in pregnancy and is the leading cause of intracranial hemorrhage in full-term infants. FNAIT results from the formation of maternal antibodies targeting fetal platelet antigens.  Antibody formation to human platelet antigen 1a (HPA-1a) accounts for 75% to 80% of severe cases of FNAIT.  FNAIT is difficult to diagnose, and there are currently no approved therapies.  To better understand predictors of FNAIT and capture antibody-negative cases, researchers in Canada followed a cohort of 131 mothers who gave birth to infants with suspected FNAIT.  Clinical predictors of severe FNAIT were evaluated in 55 women with 72 subsequent pregnancies; 15 infants had severe FNAIT, including 10 infants with platelet counts <20 X 10⁹ /L, two infants with intracranial hemorrhage, and three infants who died.  The presence of HPA-1a antibodies during the first pregnancy was the only significant predictor of severe FNAIT identified, but one infant with an antibody-negative mother still developed severe FNAIT. Furthermore, weekly antenatal intravenous immune globin (IVIG) treatment did not prevent all cases of severe FNAIT.  During subsequent pregnancies, 58.3% (42/72) of mothers received weekly treatments with IVIG, but 24% of infants still developed FNAIT compared to 20% of infants whose mothers did not receive IVIG (p=0.88).  A new prophylactic treatment for FNAIT with HPA-1a specific antibodies prevents FNAIT in animal models and may be evaluated in clinical trials soon.  Further research is needed to better understand the clinical predictors and the most effective preventive measures for FNAIT.

References:

1. Matusiak K, Patriquin CJ, Deniz S, Dzaja N, et al.  Clinical and laboratory predictors of fetal and neonatal alloimmune thrombocytopenia.  Transfusion 2022; 26; 2213-2222.  
2. Zhi H, Sheridan D, Newman D, Newman P.J. Prophylactic administration of HPA-1a-specifc antibodies prevents fetal/neonatal alloimmune thrombocytopenia in mice.  Blood 2022; 140(20); 2146-2153.
3. Semple JW and R Kapur. Protecting the fetus from FNAIT.  Blood 2022; 140(20); 2097-2099.