Noninvastive prenatal diagnosis by the isolation and analysis of fetal cells in maternal blood is now possible. To date, results suggest that low numbers of fetal cells are present in 20 ml samples. This study was performed to determine if intrinsically low numbers of fetal cells exist in maternal whole blood samples or if there are initially higher numbers that are progressively lost during fetal cell separation techniques.

Peripheral venous samples were collected from 210 pregnant women and subjected to a whole blood lysis DNA extraction. PCR amplification of a Y chromosome sequence (49a) was used as an indication of the number of fetal cells originating in male fetuses. Reaction products were separated by electrophoresis, phosphorimaged, and compared to results of amplification using known amounts of male DNA. For negative controls, nonpregnant female samples were also analyzed. Values were normalized to represent the equivalent number of fetal cells in two 8 ml vacutainers.

Results Table

Table 1
Full size table

These results indicate significant differences exist in the number of fetal cells detected in 46,XY versus 47,XY,+21 or other male abnormal karyotypes(p<0.001 and <0.05, respectively, by one way ANOVA). Results from the negative controls suggest that the of low numbers of male cells in some 46,XX pregnancies is due to residual cells circulating from prior male pregnancies or transfusions. Low, although analyzable, numbers of male fetal cells are present when the fetus is normal, but significantly more cells are detectable when the fetus is aneuploid. This implies that routine noninvasive detection of fetal aneuploidy should be feasible. Funded by a research grant from Integrated Genetics to Dr. Bianchi.