Isoimmunization: Management

MANAGEMENT

Previously, blood was transfused into the fetal abdomi-nal cavity, where absorption of the red cells could take place over several days through the lymphatic channels. 

Currently, transfusion of antigen-negative red blood cells (depending on the blood group involved) to the fetus is indicated when PUBS determines that the fetus has mod-erate or severe anemia with a hematocrit less than 30%. Direct transfusion under ultrasound guidance into the umbilical vein has become the preferred technique. The procedure has a1% to 3% risk of complications, including fetal death and preterm delivery, which must be weighed against the pre-dicted course of the fetus if left untreated or delivered. The volume of red blood cells to be transfused can be calculated based on the gestational age, estimated fetal weight, the hematocrit of the unit of blood, and the differ-ence between the current fetal hematocrit and the desired hematocrit. Because the transfused cells are antigen-negative, they are not subject to hemolysis by the mater-nal antibody and the predicted lifespan of the red cell is the only determinant of how long they persist in the fetal circulation. The timing and need for further transfusions can be based either on the predicted course given the severity of the disease, or on MCA Doppler assessments. After 2 to 3 transfusions, most of the circulating red cells in a fetus are transfused cells, as the hematopoietic system in the fetus has been suppressed.

Box 19.1

Evaluation of a Pregnancy With a Positive Maternal Antibody Screen

Maternal antibody identification and titer Careful obstetric history for prior affected fetus

Paternal antigen testing, possible fetal DNA

testing

Assessment of risk for fetal anemia if a critical

titer is found or if there has been a prior affected child

Amniotic fluid bilirubin assessment

Serial antibody titers, if first sensitized pregnancy Middle cerebral artery Doppler Ultrasound

Cordocentesis/percutaneous umbilical blood

sampling if monitoring test is abnormal