Fetal survival and development is supported by the maternal immune system. Questions regarding those mechanisms have risen from development of transplantation medicine and observation of graft rejection. Initial theories of anatomic division, fetal immune immaturity and maternal immune system inertia were found incorrect. Rejection of fetal "semi-allograft" by maternal immune system could result in pregnancy loss. Two pregnancy losses of any etiology are considered recurrent and effort should be made to name the probable cause. Immune causes of pregnancy loss are probably multifactorial, thus difficult to research and implement findings in clinical practice. Although a full understating of pregnancy loss is not established, new therapies are being developed. This review summarizes the role of lymphocytes in pregnancy develop- ment, presents data from studies on recurrent pregnancy loss patients, evidence of new therapies and ESHRE guidelines regarding immunologic investigations.
Keywords: Th17; Treg; abortion; habitual; lymphocytes; recurrent pregnancy loss; uNK.