Decidual cytokines and pregnancy complications: focus on spontaneous miscarriage

• Background to decidual cytokines and miscarriage.
• Background to trophoblast invasion, spiral artery remodelling and immune tolerance.
• Discussion of the role of inadequate trophoblast invasion/spiral artery remodelling in miscarriage.
• Discussion of decidual cytokine dysregulation and spontaneous miscarriage.

The establishment of pregnancy requires the co-ordinated implantation of the embryo into the receptive decidua, placentation, trophoblast invasion of the maternal decidua and myometrium in addition to remodelling of the uterine spiral arteries. Failure of any of these steps can lead to a range of pregnancy complications, including miscarriage, pre-eclampsia, fetal growth restriction, placenta accreta and pre-term birth. Cytokines are small multifunctional proteins often derived from leucocytes and have primarily been described through their immunomodulatory actions. The maternal–fetal interface is considered to be immunosuppressed to allow development of the semi-allogeneic placental fetal unit. However, cytokine profiles of the decidua and different decidual cell types suggest that the in vivo situation might be more complex. Data suggest that decidual-derived cytokines not only play roles in immunosuppression, but also in other aspects of the establishment of pregnancy, including the regulation of trophoblast invasion and spiral artery remodelling. This review focuses on the potential role of decidua-derived cytokines in the aetiology of unexplained spontaneous miscarriage.