Blocking antibodies In the serum of normal pregnant women, there is a specific IgG antibody against the mate’s lymphocytes that inhibits the lymphocyte response (MLR), shuts down the cytotoxic effect of maternal lymphocytes on the cultured trophectoderm, prevents the recognition of suppressors of fetal antigens by helper T cells, and prevents the attack of the mother’s immune system on the embryo. Blocking alloantigen-stimulated lymphocytes produce macrophage movement inhibitory factor (MIF), so it is called blocking antibodies (BA). Immunotherapy In patients with recurrent spontaneous abortion, an APLA (blocking antibodies) test is performed first, and if the APLA is negative, active immunotherapy with the husband’s lymphocytes is used. The specific course of treatment is 3-4 injections prior to pregnancy, recheck APLA, and plan conception if APLA turns positive (including ovulation monitoring, ovulation promotion, artificial insemination, IVF, etc.).