Objective: Since immunoglobulin is transported across the placenta, maternal administration of、it theoretically seems attractive as an antenatal treatment for a fetus. However, the effects of antenatally administered intravenous immunoglobulin (IVIG) on fetal platelet counts have been controversial. Our series of 11 cases of idiopathic thrombocytopenic purpura (ITP) and a review of previous reports are presented. A combined retrospective analysis to know whether maternal response to IVIG is associated with improvement of fetal thrombocytopenia was conducted. Methods: IVIG was given to 11 steroid refractory pregnancies with ITP. Good maternal response to the therapy was defined as an increase in the platelet count to greater than 50 × 10⁹/L after completion of the IVIG infusion. Neonatal platelet counts of the umbilical cord were performed just after birth and followed-up for at least the first week of life. Results: Seven of the 11 neonates had thrombocytopenia of less than 100 × 10⁹/L, and two of them had severe thrombocytopenia of less than 50 × 10⁹/L. Two out of two neonates born to mothers with a good response to IVIG were thrombocytopenic; whereas five out of nine neonates born to mothers with a poor response were thrombocytopenic. The combined retrospective analysis of our results and published reports have shown that fetal thrombocytopenia was not associated with the maternal response to IVIG but with the level of immunoglobulin G of neonates at birth. Passive thrombocytopenia was more frequently observed in neonates with normal levels of immunoglobulin G than those with elevated levels. Conclusion: This combined analysis confirmed the proposed hypothesis that the lack of effect of maternally administered IVIG on fetal platelet counts may mainly be attributed to the insufficient therapeutic level of transferred immunoglobulin G in the cord blood.