APLN and gestational diabetes: Analysis of 20 studies, including 1493 GDM patients and 1488 normal pregnant women did not find significant differences in circulating apelin and chemerin levels (apelin standardized mean difference [SMD] = 0.43, 95% confidence interval (CI): − 0.40 to 1.26, P = 0.31; chemerin SMD = 0.77, 95% CI − 0.07 to 1.61, P = 0.07).