TNFSF13B and abortion: First, BAFF is essential for B‐cell survival and the differentiation of immature transitional B cells into mature naïve cells, and BAFF is an important immune regulator that has been reported to be secreted by the placenta.47, 48 A previous study demonstrated that BAFF exhibits higher expression in the trophoblasts and decidua of normal early pregnant women than in the tissues of recurrent spontaneous abortion patients,49 confirming that BAFF may be an essential element in the implantation of the embryo and maintenance of pregnancy.