Fetal ABO blood group typing using amniotic fluid.

Abstract

Amniotic fluids (AF) obtained by second trimester amniocentesis were examined using a hemagglutination‐inhibition test. In the anti‐A and anti‐B dilution series three different patterns of agglutination were found. One pattern, indicating the presence of high levels of antigen, is typical of secretors (Se/‐) of the blood group antigen. The second pattern is indicative of total absence of soluble antigen and is produced in secretor (Se/‐) and non‐secretor (se/se) fetuses lacking the IA or IB allele at the ABO locus. The third pattern shows the presence of trace amounts of soluble antigen, about one‐tenth of that found in secretors, and it appears in non‐secretor fetuses bearing the corresponding ABO allele. These trace quantities, if a constant feature of AFs from these non‐secretor fetuses, could allow blood group typing information to be obtained on all non‐secretor as well as secretor fetuses.A total of 157 amniotic fluid samples were surveyed in this and a previous study. Of these, 31 were from non‐secretor fetuses. Blood group type for the 31 non‐secretor fetuses was predicted (“blindly”) on the basis of the presence or absence of trace amounts of soluble antigen. These predictions were verified by standard ABO typing of the infants afterbirth. In each case the (“blind”) typing result agreed with the predictions made from the titration curves. This agreement establishes that the production of trace amounts of soluble antigen(s) is a consistent feature of non‐secretors with the IA and/or IB allele. The soluble blood group substances are of fetal origin and are independent of maternal blood type and secretor status. Type O non‐secretors produce no soluble A or B antigen and also lack detectable soluble H antigen. Thus it appears that the nature of the detectable amounts of soluble blood group antigen(s) present in second‐trimester AF can be used to accurately assess the ABO blood type of all fetuses.