The present invention provides systems, apparatuses, and methods to isolate, select or detect the presence of a target cell (e.g., fetal cells) in a sample comprising mixed populations of cells that vastly outnumber the target cells. Target cells include fetal cells, such as nucleated red blood cells, and methods of selecting such cells include diagnosis of fetal abnormalities, i.e., aneuploidy. Furthermore, methods comprise utilizing fetal biomarkers to select fetal cells in a sample comprising fetal and adult cells.