After adjusting for thalassemia and hemoglobinopathies commonly observed in this region, we found that G6PD deficiency, G6PD ViangchanG871A, female gender, neonatal anemia (Hb < 15 g/dL), ABO incompatibility, and postpartum age were independent factors promoting reticulocytosis in newborns. This evidence concerns the gene GSTM1 and thalassemia.