Fetal cells in the maternal circulation: isolation by multiparameter flow cytometry and confirmation by polymerase chain reaction.

During pregnancy, nucleated fetal erythrocytes enter the maternal circulation and can be isolated efficiently from the maternal cells by multiparameter flow cytometry. Male DNA, implying presence of a male fetus, can be identified in flow-sorted maternal blood by polymerase chain reaction with oligonucleotide primers flanking single-copy Y-specific DNA sequences. Among flow-sorted samples, we correctly identified fetal sex in 17/18 (94%) pregnancies of 10-21 weeks gestation. Maternal blood thus provides a potential opportunity for prenatal diagnosis that could preclude the need for invasive procedures in current use.