After 12-weeks gestational age, a dose of 300 mcg is recommended. This dose will suppress the immune response to 2.5 mL of Rh-positive red blood cells. Before 12-weeks gestational age, in the setting of an RhD negative mother and FMH, a mini-dose of 150 mcg Rho(D) immune globulin is given. To prevent the formation of anti-RhD antibodies, Rho(D) immune globulin is indicated. Future pregnancies may be at risk for RhD disease if the fetus is RhD positive. The maternal antibodies bind to fetal RhD positive erythrocytes, leading to hemolysis, anemia, hydrops fetalis, and possibly fetal death. It takes only 0.01 ml to 0.03 ml of FMH for the isoimmunization of the mother. In response to this exposure, the maternal immune system is activated, and isoimmunization (formation of anti-RhD antibodies) may occur if the mother is Rhesus-D protein (RhD) negative and the blood type of the fetus is RhD positive. When FMH occurs, fetal hemoglobin (HbF) is mixed with maternal blood. It occurs in as many as 40% of traumas, increasing in frequency and amount with high-force trauma, blunt force trauma, abdominal trauma, and anterior placental placement in the uterus. Trauma is the number one cause of pregnancy-associated maternal deaths in the United States. This disruption in the placental barrier may occur for many reasons, including intrauterine fetal demise and trauma. Fetomaternal hemorrhage (FMH) occurs when there is a break in the placental barrier, allowing blood from the fetal circulation to enter the maternal circulation.
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