TFRC and gestational diabetes: Thirty studies examined the association between serum ferritin (SF) levels [24–30, 32–47, 51, 54, 55, 57, 59–61] and the risk of GDM; 18 studies assessed the relationship between serum iron (SI) [27, 31, 32, 34, 35, 37, 39, 43, 45–49, 51, 52, 56, 58, 63] and GDM; five studies with TIBC [26, 30, 33, 38, 47], four studies with serum transferrin receptor (sTfR) [24, 27, 28, 59], and four studies with transferrin [36, 37, 47, 48] were selected for the meta-analyses.