Fetal cells may be obtained from amniocentesis, chorionic villus sampling, percutaneous umbilical cord sampling or in vitro fertilization embryos or products of conception, but are preferably from maternal peripheral blood. Fetal cells may be enriched by density gradient centrifugation. Fetal cells may also be enriched by removing maternal cells with an antibody to a cell surface antigen, e.g. anti-CD45, either immobilized or by fluorescence-activated cell sorting. Fetal cells are also distinguishable from maternal cells by staining, e.g. with a labeled antibody to cytokeratin or to fetal hemoglobin, or for fetal hemoglobin by hematoxylin/eosin, or by in situ hybridization to detect one or more fetal mRNAs, e.g., of fetal hemoglobin or fetoprotein. Amplification may be used in conjunction with the in situ hybridization. Fetal cells circulating in maternal blood may be separated by flow cytometry, sorting on their intrinsic light scattering properties. Fetal nucleated erythrocytes may be identified by a label for fetal hemoglobin. Fetal cells may be treated to determine genetic characteristics or abnormalities, infectious agents or other properties by nucleic acid hybridization. Genetic abnormalities may include deletions, additions, amplifications, translocations or rearrangements. Multiple abnormalities may also be detected simultaneously, and they may be visually distinguished by color. Kits are provided for the disclosed procedures.
Assays for target molecules in and from cells and viruses, e.g. nucleic acids, wherein non-specific background is decreased by including an analogue of the reporter group, e.g. a non-fluorescent analogue such as fuchsin, of a fluorescent group such as fluorescein, to decrease non-specific backround.