3-HAA: 3-hydroxyanthranilic acid; 3-OH-KYN: 3-hydroxykynurenine; AA: anthranilic acid; DMT1: diabetes mellitus type 1; DMT2: diabetes mellitus type 2; GDM: gestational diabetes mellitus; HLA: human leukocyte antigen; HOMA-IR: homeostatic model assessment for insulin resistance; IDO: indoleamine 2,3-dioxygenase; KATs: kynurenine aminotransferases; KYN: kynurenine; KYNA: kynurenic acid; QUIN: quinolinic acid; Trp: tryptophan; XA: xanthurenic acid. Here, IDO2 is linked to gestational diabetes.