Evaluation of the Clinical Usefulness of Isolation of Fetal DNA From the Maternal Circulation

Abstract

Because current prenatal diagnostic techniques are invasive and can cause miscarriage, the authors evaluated a procedure involving the isolation of free fetal DNA from maternal plasma or serum. Samples were taken prospectively from 24 women having prenatal diagnostic procedures, most often chorionic villous sampling, in the late first or second trimester. Samples also were obtained from 28 Rhesus-negative women in whom blood had previously been taken for triple serum screening. DNA was extracted and assayed for the β-globin gene, the sex-determining region Y (SRY) gene, and the Rh gene using the polymerase chain reaction (PCR) technique. All samples contained a key β-globin sequence that indicated the presence of sufficient DNA. When the SRY PCR findings were compared with the fetal cell karyotypes obtained by invasive testing, all but 3 of 24 samples were correctly sexed. In comparison of the RhD PCR results to fetal cord blood samples taken at delivery, both false-positive and false-negative results were obtained. Two RhD-negative infants were genotyped as RhD-positive, even on repeat analysis. It clearly is possible to isolate fetal DNA from maternal serum and to detect male fetuses and Rh-negative fetuses. It is important to use the optimal range of PCR primers available to cover polymorphisms within the RhD gene. It also is necessary to take measures to prevent contamination when handling samples. The investigators believe that, with expected technical improvements, new probes, and real-time PCR equipment, this diagnostic approach will soon become a practical one. It has the advantages of being rapid, potentially reliable, and relatively easy to perform.