In the subgroup analysis of the average age, GDM patients with mean age < 30 years had significantly increased circulating chemerin levels when compared with controls (SMD: 2.30; 95% CI: 0.69, 3.91); however, the difference was not significant between patients with mean age ≥ 30 years and controls (SMD: 0.12; 95% CI: − 0.11, 0.35); significantly decreased heterogeneity was observed in the group of age ≥ 30 years (I2 = 28.2%, P = 0.223), but not in the group of age < 30 years (I2 = 98.7%, P < 0.001) (Fig. 6). Here, RARRES2 is linked to gestational diabetes.