In early pregnancy, two immune transformations occur: (a) interleukin-10 (IL-10), interleukin-13 (IL-13) increased at day 5, which promoted immunoglobin G (IgG) secretion, provided protection through the neonatal Fc receptor for IgG (FcγRn) crossing the placental barrier to reach the embryo, achieved T helper 1 (Th1) transformation into T helper 2 (Th2), reduced maternal innate and cellular immunity, and prevented fetal abortion; (b) the fetal heart was fully developed at day 7, with circulatory system established, which provided a platform for intercellular information exchange. The gene discussed is IL13; the disease is abortion.