Neonatal alloimmune thrombocytopenia due to anti-HPA 1a antibodies; the level of maternal antibodies predicts the severity of thrombocytopenia in thenewborn

Eleven thousand one hundred pregnant women were genotyped for human platele t antigen HPA 1, and 198 HPA 1bb women were followed in the pregnancy with quantitative assay for anti-HPA la antibodies. Antibodies were detected in 24 women, and nine children were born with severe thrombocytopenia (< 50x10 (9)/L). All mothers with high levels of antibodies were delivered of childr en with severe thrombocytopenia. None of the newborn infants had clinical s igns of intra-cranial haemorrhage. The level of maternal anti-HPA la antibo dies is predictive for fetal thrombocytopenia and may be used in decisions related to time and mode of delivery.