Sirolimus as a new drug to treat RIF patients with elevated Th17/Treg ratio: A double-blind, phase II randomized clinical trial.

Background: RIF is clinically defined as the failure of good quality embryos to implant into the uterus following at least three cycles of In Vitro Fertilization/Embryo Transfer (IVF/ET). During human pregnancy, a genetically different fetus is allowed to survive within the uterus despite the maternal recognition of fetal alloantigens. Compared with normal pregnant women, early loss of embryo is associated with systemic lower levels of Treg cells in IVF.