MTNR1B and gestational diabetes: Our meta-analysis included the alleles in IGF2BP2, MTNR1B, TCF7L2, IRS1, TNF-α, and PPARG genes, and showed the risk alleles of MTNR1B, TCF7L2 and IRS1, but not PPARG, were significantly associated with increased risk of GDM with or without study heterogeneity, HWE derivation and publication bias.