A new 12-year-long study in the Australian and New Zealand Journal of Obstetrics and Gynecology analyzed over 62,000 routine cord blood platelet counts to find out how often severe fetal neonatal alloimmune thrombocytopenia (FNAIT) occurred in otherwise healthy term infants.
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Researchers found that while mild thrombocytopenia was not uncommon, severe thrombocytopenia suggestive of FNAIT was detected in only a very small number of newborns.
Eight infants were diagnosed with confirmed or suspected NAIT, accounting for just 0.013% of all infants with usable cord blood results. The majority of confirmed cases involved anti–HPA-1 antibodies and were seen in families of European descent. Only two potential cases were found among Māori and Pacific Island infants, but neither had follow-up testing to verify NAIT.
“Severe thrombocytopaenia potentially due to NAIT was very rare in infants of Maori and Pacific Island ethnicity,” the authors wrote, noting that platelet antigen patterns vary across populations and may influence risk.
The long-term study also examined platelet counts in siblings of affected infants to analyze recurrence patterns. Of the 327 siblings with available data, only 5% had low platelet counts, and severe thrombocytopenia was usually linked to known FNAIT or maternal immune conditions.
Although severe FNAIT can pose significant bleeding risks, including the chance of intracranial hemorrhage, no cases of serious bleeding or death occurred during the 12-year study. Only two infants with confirmed NAIT needed treatment, and most infants with potential NAIT showed no symptoms.
The authors concluded that routine cord blood platelet testing in symptom-free full-term infants offers limited benefit for detecting severe FNAIT in this diverse hospital population. Classic HPA-1–associated disease was rare outside families of European descent. They highlighted the potential advantage of collecting more comprehensive data to better understand FNAIT risk in underrepresented groups.
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