Although these results are encouraging, fetal platelet count is not always increased with maternal high-dose immunoglobulin infusion, even with a documented increase in fetal immunoglobulin levels.     One problem with maternally administered IgG is that it may not cross the placenta effectively prior to 32 weeks gestation.  Also, intravenous immunoglobulin is quite expensive (over $1,000 per weekly infusion), and the infectious risk (albeit small) of blood product infusion is highlighted by the recent outbreak of acute hepatitis C associated with use of some brands of intravenous immunoglobulin. 
In the management of patients at risk for alloimmune thrombocytopenia, we offer weekly infusions of intravenous immunoglobulin beginning at 20 to 24 weeks' gestation after a full discussion of the risks and potential benefits and after cordocentesis to confirm fetal thrombocytopenia. For those whose fetal platelet count is normal, and for those who decline umbilical blood sampling and immunoglobulin treatment, we advocate bedrest with avoidance of abdominal trauma and serial sonograms during the third trimester to detect intracranial bleeding. Regardless of the regimen used, all patients undergo cordocentesis at 36 to 37 weeks gestation to determine the fetal platelet count. If the fetal platelet count is greater than 50,000 cells/mul, labor is induced. If the fetal platelet count is less than 50,000 cells/mul, immediate platelet tranfusion into the umbilical vein, with documentation of an adequate post-transfusion platelet count, is followed by induction of labor.
Patients with a previous severely thrombocytopenic fetus and significant antepartum morbidity are generally offered surveillance at an earlier gestational age, but the risks of repeated umbilical blood sampling and serial platelet transfusions do not seem to be warranted except in extreme cases. If the fetus remains severely thrombocytopenic (<50,000 platelets/mul) in spite of attempts to raise the platelet count, cesarean delivery is preferred.
In all cases of documented fetal-neonatal alloimmune thrombocytopenia, maternal platelets should be available for transfusion after delivery, regardless of the treatment protocol used or the antepartum fetal platelet count.
Determination of platelet antigen genotypes using polymerase chain reaction has been described,   and reports of diagnosis of fetal platelet antigen status from uncultured amniocytes obtained at amniocentesis should be forthcoming. As with Rh disease, this advance will allow determination of fetal antigen status (and risk of thrombocytopenia) in sensitized pregnancies without umbilical cord blood sampling. Also in the very near future, preimplantation genetic testing will be available, given the ability to determine genotype from a single cell.
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