S U M M A R Y Current cytogenetic approaches in noninvasive prenatal diagnosis focus on fetal nucleated red blood cells in maternal blood. This practice may be too restrictive because a vast proportion of other fetal cells is ignored. Recent studies have indicated that fetal cells can be directly detected, without prior enrichment, in maternal blood samples by fluorescence in situ hybridization (FISH) analysis for chromosomes X and Y (XY-FISH). In our blinded analysis of 40 maternal blood samples, we therefore examined all fetal cells without any enrichment. Initial examinations using conventional XY-FISH indicated a low specificity of 69.4%, which could be improved to 89.5% by the use of two different Y-chromosome-specific probes (YY-FISH) with only a slight concomitant decrease in sensitivity (52.4% vs 42.9%). On average, 12-20 male fetal cells/ml of maternal blood were identified by XYand YY-FISH, respectively.

S U M M A R YWe performed a comparative study of the enrichment of erythroblasts by a soybean agglutinin galactose-specific lectin method and a standardized magnetic cell-sorting (MACS) protocol. Blood samples, obtained from 11 pregnant women at between 11 and 40 weeks of gestation, were split and examined by each method in parallel. The number of erythroblasts recovered by the lectin method was approximately eightfold higher than the number obtained by MACS. Our data suggest that the lectin-based method may provide a better approach for the enrichment of rare fetal erythroblasts from maternal blood.

Male fetal cells can be detected in most maternal blood samples examined. Specificity and sensitivity is improved when using a combination of single X and two Y chromosome-specific probes when compared to a conventional XY-FISH protocol.

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