The risk of antibody formation against HNA1a and HNA1b granulocyte antigens during pregnancy and its relation to neonatal neutropenia

The evaluation of immunization by the HNA1a and 1b antigens during pregnanc y was based on (i) their genotyping in 1038 unselected mothers and newborns of homozygous mothers, (ii) granulocyte counting in all born infants and ( iii) examination of granulocyte antibodies in maternal sera if an HNA1 inco mpatibile child was born. A total of 548 (52.8%) mothers were heterozygous - thus further examinations were not done. Four hundred and ninety (47.2%) were homozygous, of whom 203 (41.3%) delivered an incompatible child, i.e. 19.6% of all the infants. Among available sera from 195 mothers with feto-m aternal incompatibility, the granulocyte-specific antibodies were found in nine (4.5%); six of these (3%) were HNA1 (four anti-1a, two anti-1b), and i n three others the specificity was not determined. In the remaining 28 sera , the only antibodies detected were HLA. Hence, six out of 1000 pregnant wo men can be expected to develop anti-HNA1. In none of the newborns was the c ord neutrophil count below 1.5 x 10(9) L-1 and signs of infection found, th us the incidence of NAIN seems to be lower than 1 per 1000 infants. A compa rison with our previous, unpublished data suggests that the incidence of se vere NAIN is roughly 1 per 6000 (four cases among 24101 newborns).