The Abstract of the study was to examine placental histopathology in intravenous immunoglobulin-treated and untreated neonatal alloimmune thrombocytopenia and correlate pathological findings with clinical outcomes. Study design: Placentas from 14 neonatal alloimmune thrombocytopenia-affected pregnancies were identified. Maternal antepartum treatment with intravenous immunoglobulin and pregnancy outcomes were Abstracted from medical records. Placental histopathology and clinical outcomes were compared between intravenous immunoglobulin and no intravenous immunoglobulin treatment groups using Fisher’ s exact test. One subject, treated only after an intracranial hemorrhage (ICH) was diagnosed, was excluded from the analysis. P< .05 was considered significant. Results: Untreated pregnancies demonstrated a lymphoplasmacytic chronic villitis not seen in the intravenous immunoglobulin-treated pregnancies (P = .005). Intrauterine growth restriction and intrauterine fetal demise occurred as frequently as ICH in the untreated group. No ICH, intrauterine growth restriction, or intrauterine fetal demises occurred in the treated group, although the P value was not significant. Conclusion: Chronic villitis is frequently manifest in neonatal alloimmune thrombocytopenia, with intravenous immunoglobulin alleviating this inflammatory immunologic response. We suspect a more universal role for the maternal antibody, such as fetal endothelial cell damage, in the sequelae of neonatal alloimmune thrombocytopenia. The Abstract of the study was to examine placental histopathology in intravenous immunoglobulin-treated and untreated neonatal alloimmune thrombocytopenia and correlate pathological findings with clinical outcomes. Study design: Placentas from 14 neonatal alloimmune thrombocytopenia-affected pregnancies were identified. Maternal antepartum treatment with intravenous immunoglobulin and pregnancy outcomes were Abstracted from medical records. Placental histopathology and clinical outcomes were compared between intravenous immunoglobulin and no intravenous immunoglobulin treatment groups using Fisher’s exact test. One subject, treated only after an intracranial hemorrhage (ICH) was diagnosed, was excluded from the P <.05 was considered significant. Results: Untreated pregnancies demonstrated in lymphoplasmacytic chronic villitis not seen in the intravenous immunoglobulin-treated pregnancies (P = .005). Intrauterine growth restriction and intrauterine fetal demise occurred as fre quently as ICH in the untreated group. No ICH, intrauterine growth restriction, or intrauterine fetal demises occurred in the treated group, although the P value was not significant. Conclusion: Chronic villitis is frequently manifest in neonatal alloimmune thrombocytopenia, with intravenous immunoglobulin alleviating this inflammatory immunologic response. We suspect a more universal role for the maternal antibody, such as endothelial endothelial cell damage, in the sequelae of neonatal alloimmune thrombocytopenia.