A method for detecting the presence or absence of Rh positive fetal cells in a liquid maternal blood sample comprising Rh negative cells from an Rh negative woman suspected of containing Rh positive fetal cells and suspected of requiring the administration of a dose of an Rh immunoglobulin to prevent a future Rh immunization which comprises: a) providing in a reaction vessel the liquid maternal blood sample comprising an Rh negative cell sample from said Rh negative woman suspected of containing Rh positive fetal cells therein to be detected; b) adding to the reaction vessel an agglutinating IgM anti-D antibody reactable with the Rh positive fetal cells sought to be detected and capable of forming a complex with said Rh positive fetal cells sought to be detected, such that a liquid mixture is formed; c) incubating said liquid mixture to allow said Rh positive fetal cells to react with said agglutinating IgM anti-D antibody to form complexes and aggregates therewith to form an incubated reaction mixture; d) transferring the incubated reaction mixture to a test vessel comprising a transparent or opaque separating solution, wherein the test vessel is a separate vessel from the reaction vessel, or the reaction vessel and test vessel are an integral set; e) Causing said aggregates and complexes to move by gravity through said separating solution to a site in said test vessel comprising an Rh positive fetal cell volume measuring zone, whereby said aggregates and complexes are deposited at said site, said separating solution retarding the movement of unreacted maternal Rh negative cells with the movement of said complexes and aggregates and retain the unreacted maternal Rh negative cells in the separating solution; f) observing the cell volume measuring zone to detect the presence or absence of deposited cell aggregates and complexes; wherein the presence of deposited cell aggregates and complexes in step f) indicates the detection of a fetal maternal hemorrhage. a) providing in a reaction vessel the liquid maternal blood sample comprising an Rh negative cell sample from said Rh negative woman suspected of containing Rh positive fetal cells therein to be detected; b) adding to the reaction vessel an agglutinating IgM anti-D antibody reactable with the Rh positive fetal cells sought to be detected and capable of forming a complex with said Rh positive fetal cells sought to be detected, such that a liquid mixture is formed; c) incubating said liquid mixture to allow said Rh positive fetal cells to react with said agglutinating IgM anti-D antibody to form complexes and aggregates therewith to form an incubated reaction mixture; d) transferring the incubated reaction mixture to a test vessel comprising a transparent or opaque separating solution, wherein the test vessel is a separate vessel from the reaction vessel, or the reaction vessel and test vessel are an integral set; e) Causing said aggregates and complexes to move by gravity through said separating solution to a site in said test vessel comprising an Rh positive fetal cell volume measuring zone, whereby said aggregates and complexes are deposited at said site, said separating solution retarding the movement of unreacted maternal Rh negative cells with the movement of said complexes and aggregates and retain the unreacted maternal Rh negative cells in the separating solution; f) observing the cell volume measuring zone to detect the presence or absence of deposited cell aggregates and complexes;