Fetal and neonatal alloimmune thrombocytopenia (FNAIT) occurs in the setting of maternal anti-human platelet antigen (anti-HPA) antibodies against paternally derived fetal platelet antigens. Recent studies have also demonstrated an association between chronic placental inflammation and FNAIT, specifically low-grade chronic histiocytic intervillositis (CHI). We present a neonate with profound thrombocytopenia after delivery with co-occurring CHI, whose platelet counts recovered rapidly with platelet transfusions, born to a primigravida mother with late-onset preeclampsia.

A male neonate was born at 40 weeks to a mother who had no known history of pregnancies, miscarriages, or transfusions. The mother developed severe preeclampsia during the induction of labor. Shortly after delivery, a physical exam of the infant showed inappropriate bruising on the heels of both feet, scattered petechiae on the hard palate, a hematoma on the left thigh after a vitamin K shot, and a bruise on the upper left abdomen. His platelet count was found to be 7,000. Platelet count rose to 94K by day 3 of life following transfusions. Placental pathology confirmed CHI. Maternal testing revealed anti-HPA-1 antibodies supporting FNAIT.

This case highlights a potential relationship between maternal alloimmune response and preeclampsia. It also highlights the importance of considering FNAIT as a diagnosis in a neonate presenting with thrombocytopenia regardless of maternal preeclampsia, and the importance of submitting the placenta for a pathology exam.

The corresponding author is the guarantor of the submission.

H.W.: groups 1 and 2. A.S.: groups 2 to 4.

Received: 16 May 2025

Accepted: 11 September 2025

Article published online:
01 October 2025

© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)

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