We aimed to investigate the clinical effect of intravenous immunoglobulin G (IVIg) treatment in recurrent aborters with elevated peripheral blood CD56+ NK cell levels while on lymphocyte immunization, anticoagulation and prednisone treatment, with respect to subsequent live birth and reproductive outcome. Thirty-three women with recurrent abortions achieved alloimmune recognition after lymphocyte immunizations. All had autoimmune abnormalities and received preconception anticoagulation and prednisone treatment. At the time of positive pregnancy testing, 18 women with normal NK cell levels (<12%) and 6 with elevated NK cell levels (>12%) continued anticoagulation and prednisone treatment, and 9 with elevated NK cell level initiated additional IVIg treatment. The live birth rates of women with elevated NK cell level (>12%) who initiated post-conception IVIg treatment in addition to anticoagulation and prednisone (100.0%), women with normal NK cell levels (<12%) who continued anticoagulation and prednisone (83.3%) and women with elevated NK cell level (>12%) who continued anticoagulation and prednisone (33.3%) are significantly different (P=0.0065). Prevalence of intrauterine growth retardation and preterm delivery among 3 study groups were not different. In conclusion, post-conception IVIg treatment significantly improves reproductive outcome in women with elevated CD56+ NK cells with pregnancy who received preconception lymphocyte immunization, anticoagulation and prednisone treatment.