MATERNAL ALLOIMMUNIZATION MANAGEMENT
Category: Child Health
Abstract : Management of maternal alloimmunization Initial attempts to suppress Rh antibody production with Rh hapten, Rh-positive RBC stroma, and administration of promethazine were unsuccessful. Extensive plasmapheresis with partial replacement using 5% albumin and intravenous immunoglobulin (IVIG) or the administration of IVIG 1 g/kg body weight weekly has been shown to be moderately effective. The mec
Management of maternal alloimmunization
Initial attempts to suppress Rh antibody production with Rh hapten, Rh-positive RBC stroma, and administration of promethazine were unsuccessful. Extensive plasmapheresis with partial replacement using 5% albumin and intravenous immunoglobulin (IVIG) or the administration of IVIG 1 g/kg body weight weekly has been shown to be moderately effective.
The mechanism of action appears to be blockage of Fc receptors on phagocytes in the fetal reticuloendothelial system. However, these techniques only postpone the need for PUBS and IVT until 20-22 weeks' gestation, when these procedures can be performed with acceptable risk.
As a rule, serial maternal antibody titers are monitored until a titer of 1:16, which indicates that a high risk of fetal hydrops is reached. For Kell alloimmunization, hydrops can occur at low maternal titers because of suppressed erythropoiesis, and thus, delta-OD 450 values also are unreliable in predicting disease severity. Amniocentesis is then performed to assess the severity, and serial delta-OD 450 values are plotted on the Liley chart to evaluate the risk of hydrops. Frequent ultrasonographic monitoring is also performed to assess fetal well-being and detect early signs of hydrops.
During the period when intrauterine peritoneal transfusion was the only means of treatment, newborns were routinely delivered at 32 weeks' gestation. This approach resulted in a high incidence of hyaline membrane disease and exchange transfusions. With the advent of IVT in utero, the general approach to the severely affected fetus is to perform IVT as required until 35 weeks' gestation, with delivery planned at term. Establishment of lung maturity is difficult in these fetuses because of contamination of amniotic fluid with residual blood during transfusion.
Liley first described IPT in 1963. A Tuohy needle is introduced into the fetal peritoneal cavity under ultrasonographic guidance. An epidural catheter is threaded through the needle. A radiopaque medium is injected into the fetal peritoneum. The proper placement is confirmed by delineation outside of bowel or under the diaphragm or by diffusion in fetal ascites. Packed RBCs that are CMV negative and irradiated, less than 4 days old, group O, Rh negative, Kell negative, and cross matched with maternal serum are injected in 10-mL aliquots to a volume calculated by the following formula:
IPT volume = (gestation in wk - 20) X 10 mL
Residual Hb in the fetus is estimated to allow for proper spacing of IPT and selection of gestation of delivery by the following formula:
Hb g/dL = 0.85/125 X a/b X 120 - c/120
In the formula, a is the amount of donor RBC Hb transfused, b is the estimated fetal body weight, and c is the interval in days from the time of transfusion to the time of donor Hb estimation.
IPT is repeated when the donor Hb is estimated to have dropped to 10 g/dL. Usually, a second IPT is performed 10 days after the first transfusion in order to raise the Hb above 10 g/dL. Then another transfusion is performed every 4 weeks until the time of planned delivery at 34-35 weeks' gestation. Fetal diaphragmatic movements are necessary in order for absorption of RBC to occur. This approach is of no value for a moribund nonbreathing fetus. Maternal complications include infection and transplacental hemorrhage, while fetal complications are overtransfusion, exsanguination, cardiac tamponade, infection, preterm labor, and graft versus host disease. Survival rates after IPT approached approximately 75% with the help of ultrasonography.
Direct IVT has become a preferred route of fetal intervention because of the higher rate of complications and limited effectiveness of IPT in a hydropic fetus. Rodeck first successfully performed IVT in 1981. With ultrasonographic guidance, a needle is introduced into an umbilical vessel, and a fetal blood sample is obtained. The blood sample is confirmed to be of fetal origin by rapid alkaline denaturation test. All the relevant fetal tests (eg, Hb, Hct, blood type, DAT, reticulocyte count, platelet count, serum albumin, erythropoietin level) are sent. If the Hb is below 11 g/dL, an IVT is started. The position of the needle is confirmed by noting the turbulence in the fetal vessel on injection of saline. The fetus is frequently paralyzed with pancuronium in order to prevent the displacement of the needle by fetal movements.
The transfusion is performed in 10-mL aliquots to a volume of 50 mL/kg estimated body weight or until Hct of 60% is reached. The procedure is discontinued promptly if cardiac decompensation is noted on ultrasonography. In addition to all the complications of IPT, umbilical vein compression has also been noted during IVT. However, IVT has many advantages, such as immediate correction of anemia and resolution of fetal hydrops, reduced rate of hemolysis and subsequent hyperinsulinemia, and acceleration of fetal growth for nonhydropic fetuses who often are growth retarded. IVT also is the only intervention available for moribund hydropic fetuses and those with anterior placenta. The risk of fetal loss is about 0.8% with IVT versus 3.5% per procedure for IPT, and the overall survival rate is 88%.
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