The “before 24 weeks” subgroup and postpartum subgroup both include only 1 study and show non-significant association between serum RBP4 level and GDM risk (before 24 weeks subgroup: SMD = -0.426, 95 % CI [-0.886, 0.870]; postpartum subgroup SMD = -0.076, 95 % CI [-0.696, 0.472]). Here, RBP4 is linked to gestational diabetes.