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

Eleven thousand one hundred pregnant women were genotyped for human platelet 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 children with severe thrombocytopenia. None of the newborn infants had clinical signs of intra-cranial haemorrhage. The level of maternal anti-HPA 1a antibodies is predictive for fetal thrombocytopenia and may be used in decisions related to time and mode of delivery.