[Fetal cells in the maternal blood: a step towards non-invasive prenatal diagnosis? Review of the literature].

Prenatal diagnosis of genetic abnormalities requires nucleated fetal cells which are currently obtained by invasive techniques such as amniocentesis, chorionic villus sampling and percutaneous umbilical blood sampling. Each of these entails a risk to the foetus and sometimes to the mother. Nucleated fetal cells have been reported to be present in maternal blood. Recovery of fetal cells from maternal blood would allow a noninvasive prenatal diagnosis. Their rarity (1 fetal cell for 10(6) to 10(8) maternal cells) presents a technical challenge. Due to the small number of fetal cells, sensitive analysis techniques such as PCR and FISH are necessary. Some degree of fetal cells enrichment in the maternal blood sample often precedes the analysis. Different techniques are used for the enrichment: discontinuous density gradient, magnetic activated cell sorting, fluorescence activated cell sorting, micromanipulator.... Several prenatal diagnosis have already been performed from maternal venous blood samples: diagnosis of gender, RhD blood genotype, Duchenne muscular dystrophy and hemoglobinopathy by PCR, diagnosis of gender and chromosome aneuploidy by FISH. Many teams are working on this subject. It is difficult to compare the studies because the techniques of enrichment and analysis vary. We review the different strategies chosen for prenatal diagnosis from maternal blood and discuss the results.