Population Prevalence and Incident HPA ‐1a Alloimmunisation in Pregnancy: A Prospective, Multi‐Ethnic, Natural History Study

OBJECTIVE: Foetal-neonatal alloimmune thrombocytopaenia (FNAIT) is a rare disease, most commonly caused by maternal alloantibodies to human platelet antigen (HPA)-1a that can result in severe bleeding. The present study was designed to determine the frequency of higher risk for HPA-1a alloimmunisation and development of FNAIT among a racially and ethnically diverse cohort of pregnant women. DESIGN: Longitudinal, prospective, non-interventional, natural history study. SETTING: Conducted across 28 sites in North America and Europe. POPULATION: Pregnant women (≥ 18 years) with no history of FNAIT. METHODS: Blood samples were collected at 10-14 weeks' gestation and a sequential screening algorithm applied: maternal HPA-1a/1b genotyping, human leukocyte antigen [HLA]-DRB3*01:01 allele status, anti-HPA-1a antibody status and foetal HPA-1 genotype. MAIN OUTCOME MEASURES: Number of women at higher risk for HPA-1a alloimmunisation (i.e., those who are HPA-1b/b, HLA-DRB3*01:01 positive, anti-HPA-1a antibody negative and carrying an HPA-1a-positive foetus) that alloimmunise. RESULTS: Of the 14 114 participants screened, 1.7% were HPA-1b/1b genotype, which varied according to race and geography. Of 24 women at higher risk for FNAIT, five were lost to follow-up with no post-partum test for alloimmunisation. At Week 10 post-partum, 2/19 higher risk participants (11%; 95% confidence interval [CI]: 1.3%, 33.1%) demonstrated anti-HPA-1a antibodies, while 17 remained negative. Pre-existing anti-HPA-1a antibodies were identified in 18 other HPA-1bb, DRB3*01:01 positive women at screening. CONCLUSIONS: This prospective study confirms the rarity of a population at higher risk for HPA-1a alloimmunisation and FNAIT, describes the risk among Black and Asian women, and establishes a rigorous methodology to assess for risk of HPA-1a immunisation.

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Journal
BJOG An International Journal of Obstetrics & Gynaecology
Published
2026-09-13
DOI
https://doi.org/10.1111/1471-0528.70326
Primary Topic
Platelet Disorders and Treatments
Type
article
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article

Population Prevalence and Incident HPA ‐1a Alloimmunisation in Pregnancy: A Prospective, Multi‐Ethnic, Natural History Study

Sara Alson, Emilie Vander Haar, Surabhi Nanda, Russell S. Miller et al.
BJOG An International Journal of Obstetrics & Gynaecology
Platelet Disorders and Treatments
article

Population Prevalence and Incident HPA ‐1a Alloimmunisation in Pregnancy: A Prospective, Multi‐Ethnic, Natural History Study

Sara Alson, Emilie Vander Haar, Surabhi Nanda, Russell S. Miller, Helena Litorp, E. J. T. Verweij, E Schleußner, Vasilis Sitras, Heidi Tiller, Michael P. Bombara, James B. Bussel, Shauna Williams, Daniel W. Skupski, Katherine Kohari, Akash Gupta, Dawn Black, Laura Lawrence, Gwen Allen, Romy Pothof, Robin Perry, Kristy Palomares, Michael Paidas, Hector Mendez-Figueroa, Roisin Armstrong, Eva Wiberg‐Itzel, David Dhanraj, Laura Hart
article en

Abstract

OBJECTIVE: Foetal-neonatal alloimmune thrombocytopaenia (FNAIT) is a rare disease, most commonly caused by maternal alloantibodies to human platelet antigen (HPA)-1a that can result in severe bleeding. The present study was designed to determine the frequency of higher risk for HPA-1a alloimmunisation and development of FNAIT among a racially and ethnically diverse cohort of pregnant women. DESIGN: Longitudinal, prospective, non-interventional, natural history study. SETTING: Conducted across 28 sites in North America and Europe. POPULATION: Pregnant women (≥ 18 years) with no history of FNAIT. METHODS: Blood samples were collected at 10-14 weeks' gestation and a sequential screening algorithm applied: maternal HPA-1a/1b genotyping, human leukocyte antigen [HLA]-DRB3*01:01 allele status, anti-HPA-1a antibody status and foetal HPA-1 genotype. MAIN OUTCOME MEASURES: Number of women at higher risk for HPA-1a alloimmunisation (i.e., those who are HPA-1b/b, HLA-DRB3*01:01 positive, anti-HPA-1a antibody negative and carrying an HPA-1a-positive foetus) that alloimmunise. RESULTS: Of the 14 114 participants screened, 1.7% were HPA-1b/1b genotype, which varied according to race and geography. Of 24 women at higher risk for FNAIT, five were lost to follow-up with no post-partum test for alloimmunisation. At Week 10 post-partum, 2/19 higher risk participants (11%; 95% confidence interval [CI]: 1.3%, 33.1%) demonstrated anti-HPA-1a antibodies, while 17 remained negative. Pre-existing anti-HPA-1a antibodies were identified in 18 other HPA-1bb, DRB3*01:01 positive women at screening. CONCLUSIONS: This prospective study confirms the rarity of a population at higher risk for HPA-1a alloimmunisation and FNAIT, describes the risk among Black and Asian women, and establishes a rigorous methodology to assess for risk of HPA-1a immunisation.

BJOG An International Journal of Obstetrics & Gynaecology
Rutgers, The State University of New Jersey (US), Leiden University (NL), Uppsala University (SE), Oslo University Hospital (NO), Sunnybrook Health Science Centre (CA), St Thomas' Hospital (GB), St. Francis Medical Center (US), Saint Peter's University Hospital (US), University of Miami (US), Lund University (SE), Wright State University (US), Cornell University (US), Columbia University Irving Medical Center (US), New York Hospital Queens (US), Nordland Hospital Trust (NO), Yale University (US), Cooper Medical School of Rowan University (US), Stockholm South General Hospital (SE), Presbyterian Hospital (US), Clinical Research Consultants (United States) (US), Skåne University Hospital (SE), Medical Research Associates (US), Applied Behavioral Research (United States) (US), The University of Texas Health Science Center (US), Friedrich Schiller University Jena (DE), UiT The Arctic University of Norway (NO), Temple University (US)
Gender equality, Good health and well-being
Openalex Percentile: Top 10%
Platelet Disorders and Treatments
DOIOpen Access PDFOpenAlex
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