Feto maternal transfusion is detected by:

Kleihauer-Betke test may be performed on maternal blood to assess the amount of fetomaternal bleed.The maternal blood is subjected to an acid solution.Acid will elute the adult hemoglobin,but not the fetal hemoglobin from the red cells.Hence fetal red cells appear dark red,adult red cells appear pale(ghost cells). TEXT BOOK OF OBSTETRICS,Sheila Balakrishnan,2nd edition,page no.311