The aim of this study was to identify the association of adiponectin gene single nucleotide polymorphism (SNP) 45TG with gestational diabetes mellitus (GDM) diagnosed on the new International Diabetes in Pregnancy Consensus Group (IADPSG) criteria, plasma adiponectin levels and adverse pregnancy outcomes in Han women of Nantong area in China. This cross-sectional study included 128 pregnant women with GDM (GDM group) and 140 pregnant women with normal glucose tolerance (NGT group) according to oral glucose tolerance test results based on the new IADPSG criteria. The GDM pregnant women were treated by diet control or diet control and insulin injection. All pregnant women attended antenatal cares and were recorded until delivery. Adiponectin gene was amplified through PCR, and SNP was detected using restriction enzyme SmaI. Plasma adiponectin levels were measured by ELISA. The G allele and TG+GG genotype were significantly more frequent than the T allele in the GDM group than in the NGT group (p < 0.05). Plasma adiponectin concentrations of TG+GG genotype carriers were significantly lower than those of TT genotype in both groups (p < 0.01). After adjustment for confounding factors, plasma adiponectin level remained significantly lower in pregnant women with TG+GG genotype than those with TT genotype (p < 0.05). Compared with the NGT group, the GDM group with glycemic control still had significantly higher incidences of macrosomia, neonatal hypoglycemia and asphyxia (p < 0.05). Further analysis revealed that the incidences of macrosomia and neonatal hypoglycemia were significantly higher in pregnant women with TG+GG genotype than those with TT genotype after adjustment for potential confounders in affecting pregnancy outcomes (p < 0.05). Even though pregnant women are diagnosed as GDM according to the new IADPSG criteria, the adiponectin SNP45 may be closely correlated with the prevalence of GDM in Han women of Nantong area in China, and the allele +45G in adiponectin gene might be associated with reduced plasma adiponectin levels and adverse pregnancy outcomes.