Technical aspects of prenatal samplings and fetal transfusion

Fetal alloimmune thrombocytopenia and maternal intravenous immunoglobulin infusion

BACKGROUND

Different therapeutic approaches have been used in fetal-neonatal alloimmune thrombocytopenia, but many centers administer immunoglobulin G infusions to the pregnant woman. We studied the effect of maternal antenatal immunoglobulin infusions on fetal platelet counts in pregnancies with fetal alloimmune thrombocytopenia.

DESIGN AND METHODS

We retrospectively analyzed the clinical courses of fetuses with fetal alloimmune thrombocytopenia whose mothers were treated with immunoglobulin G infusions in a single center between 1999 and 2005. In a center-specific protocol, weekly maternal immunoglobulin G infusions were given to 25 pregnant women with previously affected neonates and four women with strong platelet antibodies, but no previous history of fetal alloimmune thrombocytopenia; before each infusion diagnostic fetal blood sampling was performed to determine fetal platelet counts and immunoglobulin G levels.

RESULTS

There were 30 fetuses with fetal alloimmune thrombocytopenia, confirmed by initial fetal blood sampling showing fetal platelet counts between 4×10(9)/L and 130×10(9)/L and antibody-coated fetal platelets using a glycoprotein specific assay. Despite weekly antenatal maternal immunoglobulin G infusions fetal platelet counts did not change significantly. Maternal and fetal immunoglobulin G levels, measured before every infusion, increased significantly with the number of maternal immunoglobulin G infusions.

CONCLUSIONS

In this group of fetuses with fetal alloimmune thrombocytopenia no consistent increase of fetal platelets was achieved as a result of regular maternal immunoglobulin G infusions.

Maternal intravenous immunoglobulin treatment does not prevent intracranial haemorrhage in fetal alloimmune thrombocytopenia

In fetal alloimmune thrombocytopenia (FAIT) the fetus is threatened by intracranial haemorrhage (ICH); therefore early diagnostic and therapeutic intervention is required. We followed the clinical course of a 30-year-old woman during her fifth pregnancy after she had given birth to a child with alloimmune thrombocytopenia due to anti-Zwa. The fetus was monitored by 13 fetal blood samplings (FBS) always followed by transfusion of either maternal or compatible donor platelets. Intravenous immunoglobulin (ivIg) treatment of the mother was begun at 20 weeks of gestation when the fetal platelet count was 36 x 10(9)/l. The fetal platelets were typed Zwa positive by DNA analysis. Despite 11 weeks of maternal ivIg treatment fetal platelet counts progressively declined to 6 x 10(9)/l and ICH occurred. Subsequently, the fetus was successfully managed by intrauterine platelet transfusions at shorter intervals (3-5 days) and elective Cesarean section was carried out at 35 weeks of gestation. We conclude that maternal ivIg treatment does not prevent ICH in FAIT. The treatment of choice for severely affected cases is serial FBS combined with transfusion of compatible platelets.

[Preparation of maternal platelets collected by separator for use in fetal transfusion in a case of alloimmunization by anti-PLA1]

In one case of fetal thrombocytopenia due to maternal immunization against PLA1 fetal platelet antigen, maternal platelets were collected by automated plasmapheresis. The platelets were collected 24 hours before fetal transfusion at 28, 29, 31 and 36 weeks of gestation. The maternal platelets were irradiated and concentrated in a small volume (7.10(10) to 1,4.10(11) plts in less than 20 ml maternal plasma) a few hours before transfusion. When prepared as described, maximal and irreversible platelet aggregation is obtained with 20 microM of ADP and the pH is over 6, 5-6 hours after concentration. The amounts of transfused platelets were determined to increase theoretically fetal platelet counts over 200,000 plts/mm3. The fetal platelet counts, determined immediately after transfusion, showed an increase of 100,000 plts/mm3. Prenatal fetal transfusion of maternal platelets is available to avoid fetal bleeding during delivery, and during the early neonatal period.

Antenatal treatment of neonatal alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia results from the formation of a maternal antibody to a paternal antigen on fetal platelets. Intracranial hemorrhage, which may be antenatal, occurs in approximately 15 to 20 percent of infants with this form of thrombocytopenia. In families with an affected infant, 75 percent of subsequent infants are affected. We report the results of antenatal treatment with intravenous gamma globulin, with or without dexamethasone, in seven pregnant women who had previously had infants who had severe alloimmune thrombocytopenia. The platelet count increased by a mean (+/- SD) of 72.5 +/- 62 x 10(9) per liter in the six fetuses in whom periumbilical blood sampling was performed. All seven treated fetuses had platelet counts above 30 x 10(9) at birth, and none had an intracranial hemorrhage, in contrast to all seven of their respective untreated siblings, who had lower platelet counts and three of whom had intracranial hemorrhages (antenatal in two infants). Mild intrauterine growth retardation was observed in one treated infant; all seven infants have developed normally in the two months to four years since birth. We conclude that intravenous gamma globulin, with or without dexamethasone, is effective in elevating the fetal platelet count in severe cases of neonatal alloimmune thrombocytopenia and in helping to avoid intracranial hemorrhage.