Circulating retinol-binding protein 4 levels in gestational diabetes mellitus: a meta-analysis of observational studies.

Retinol-binding protein 4 (RBP4) is a novel adipocyte-derived cytokine playing an important role in the regulation of energy metabolism and insulin sensitivity. Although the association between RBP4 and metabolic dysfunction is well established, studies on the relationship between circulating RBP4 levels and the risk of gestational diabetes mellitus (GDM) have yielded inconclusive results. We performed a meta-analysis to investigate whether women with GDM had higher circulating RBP4 levels than the normglycemic pregnant women. PubMed, Web of Science and EMBASE were searched up to 1 August 2014. A total of 14 studies comprised of 884 women with GDM and 1251 normglycemic pregnant women were included. The overall results suggested that maternal circulating RBP4 levels were significantly higher in GDM than their normal controls (SMD: 0.49 μg/ml, 95% CI: 0.23-0.75 μg/ml, p < 0.001, random effect model). However, stratified results indicated that this significant difference only existed in the second/third trimester and was limited to Asian populations. Furthermore, subgroup analysis according to matched maternal age and BMI still demonstrated that GDM had higher circulating RBP4 levels than the normal controls. Our findings suggested that Asian women with GDM had increased circulating RBP4 levels in their second/third trimester.