Detection and quantification of fetal red blood cells (RBCs) in maternal blood samples is essential for obstetrical management. Measurement of fetal RBCs is critical as the extent of Fetomaternal Hemorrhage (FMH), the transplacental passage of fetal RBCs into the maternal circulation, has consequences for further treatment of mother and child.

Frequency and size of FMH is directly influenced by complications in abdominal trauma, suspected placental injury or after a caesarean section. Severe FMH may lead to intra-uterine death. In case of antigen incompatibility between mother and child FMH may result in respiratory problems or anaemia, like Haemolytic Disease of the Newborn.

The detection (and thus enumeration) of fetal red blood cells (fRBCs) is used to calculate the extent of FMH, either in case of trauma with suspected placental injury or in the situation of a RhD incompatibility between the fetus and the mother. The amount of fRBCs is a measure for the prevention of hemolytic disease of the newborn using (prophylactic) anti-D therapy.