Nucleated fetal cells such as nucleated fetal red blood cells are separated from maternal blood with a discontinuous triple gradient gel and centrifugation. Nucleated fetal red blood cells are collected at an interface between a gel layer having a density in the range of from 1.105 to 1.110 g/mL and the second layer having a density in the range of from 1.075 to 1.085 g/mL, and maternal granulocytes are collected at an interface between a gel layer having a density in the range of from 1.115 to 1.125 g/mL and a layer having a density in the range of from 1.105 to 1.110 g/mL. This allows separation of fetal cells for testing from the maternal blood rather than the placenta or amniotic fluid, reducing the risk of sample collection and facilitating routine testing of fetal cells for evidence of genetic defects.