PCR QUANTITATION OF FETAL CELLS IN MATERNAL BLOOD IN NORMAL AND ANEUPLOID PREGNANCIES

Fetal cells in maternal blood are a noninvasive source of fetal geneti c material for prenatal diagnosis. We determined the number of fetal-c ell DNA equivalents present in maternal whole-blood samples to deduce whether this number is affected by fetal karyotype. Peripheral blood s amples were obtained from 199 women carrying chromosomally normal fetu ses and from 31 women with male aneuploid fetuses. Male fetal-cell DNA -equivalent quantitation was determined by PCR amplification of a Y ch romosome-specific sequence and was compared with PCR product amplified from known concentrations of male DNA run simultaneously. The mean nu mber of male fetal-cell DNA equivalents detected in 16-ml blood sample s from 30 women bearing a 46,XY fetus was 19 (range 0-31). The mean nu mber of male fetal-cell DNA equivalents detected in 109 women bearing a 46,XX fetus was 2 (range 0-24). The mean number of male fetal-cell D NA equivalents detected when the fetus was male compared with when the fetus was female was highly significant (P = .0001). More fetal cells were detected in maternal blood when the fetus was aneuploid. The mea n number of male fetal-cell DNA equivalents detected when the fetal ka ryotype was 47,XY,+21 was 110 (range 0.1-650), which was significantly higher than the number of male fetal-cell DNA equivalents detected in 46,XY fetuses (P = .0001). Fete-maternal transfusion of nucleated cel ls appears to be influenced by fetal karyotype. The sixfold elevation of fetal cells observed in maternal blood when the fetus had trisomy 2 1 indicates that noninvasive cytogenetic diagnosis of trisomy 21 shoul d be feasible.