Maternal erythrocytes in the fetal circulation. The immunocytochemical identification of minor populations of erythrocytes.

Maternal erythrocytes (Rh+) have been identified in the fetal circulation of Rh- infants by the use of a simple immunocytochemical staining technic. Placental or capillary blood from an Rh- infant of an Rh+ mother was incubated in sequence with Rh immunoglobulin, rabbit antihuman IgG, and finally goat antirabbit IgG-alkaline phosphatase conjugate. Maternal cells were found in 14% (11 of 80) of placental vein samples and 10% (2 of 20) of capillary samples. The volume of maternal blood present in the fetal circulation was calculated to be 0.06-2.3 mL with the use of placental vein samples and 0.6-1.25 mL with the use of capillary blood.