Romy Pothof

Objective: To assess the impact of vaginal deliveries on the occurrence of intracranial haemorrhage (ICH) in subsequent pregnancies with Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT). Design: Retrospective data collection. Setting: Sanquin Diagnostic Services, the national institute for diagnostic FNAIT‐testing and Leiden University Medical Center, the national referral centre for FNAIT‐management. Population: 73 subsequent pregnancies with FNAIT; 16 high‐risk and 57 standard‐risk. Methods: All women with a confirmed index pregnancy with alloantibodies against human platelet antigens (HPA) and a subsequent HPA‐incompatible pregnancy between March 1992 and February 2026 were included. Main Outcome Measures: Severe bleeding or other bleeding symptoms in neonates, associated with mode of birth. Results: There were 63 index pregnancies and 73 subsequent pregnancies, of which 72 (99%) received weekly intravenous immunoglobulin (IVIG). In the high‐risk group ( n = 16), there were 10 caesarean sections, of which four neonates had a platelet count below 50 × 10 ⁹ /L. Of the six vaginal deliveries, two neonates had a platelet count below 50 × 10 ⁹ /L. There were no bleeding complications. In the standard‐risk group ( n = 57), there were 19 caesarean sections of which eight neonates had a platelet count below 50 × 10 ⁹ /L. One ICH was identified antenatally before IVIG initiation, and three neonates developed petechiae or haematomas. Of 38 vaginal deliveries, 13 neonates had a platelet count below 50 × 10 ⁹ /L and one neonate developed petechiae. Overall (standard‐ or high‐risk), no ICH was detected in neonates delivered vaginally ( n = 44). Conclusion: No ICH was observed in HPA‐alloimmunised women who had a vaginal delivery and antenatally treated with IVIG.

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.