Figure 1.

Summary of the literature search and papers retained or excluded. ^ⱡIncluding four additional papers identified from references. ^∗Other biological samples: e.g., plasma, whole blood, CSF, and PBMCs; not pregnant or not relevant: e.g., IVF, recurrent miscarriage, fertile and infertile women, and infection or periodontitis/gingivitis; not relevant peripheral cytokines: e.g., gene polymorphisms or expression; other included not healthy pregnancy or preeclampsia and adolescent or twin pregnancy.