Although Foxp3− Treg subsets enable to repress T cell proliferation via secreting and TGF-β and IL-10 in a cell-contact independent and dependent manner as well [36], nTregs with stable Foxp3 expression are identified as the most effector Tregs activated in the decidua. Compared with iTregs, Foxp3+ nTregs acquire high immunosuppressive capacity to maintain maternal–fetal immune tolerance. In humans, low levels of circulating Treg cells have been served as a predictive signal of a risk of miscarriage in pregnant women [37]. Here, TGFB1 is linked to spontaneous abortion.