methods for determining genetic status of a fetus from a sample of maternal blood comprise enriching nucleated red blood cells in the sample , including both fetal and maternal nucleated red blood cells . the nucleated red blood cells are then differentiated from all other blood cells in the enriched sample , and the nucleated red blood cells genetically screened to determine the genetic status . the nucleated red blood cells may be differentiated by immobilizing all enriched blood cells on a solid phase and locating the nucleated red blood cells for interrogation . optionally , the nucleated red blood cells may be sorted and separated from other enriched blood cells in a liquid phase .