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Context: Gestational diabetes mellitus (GDM) affects postpartum glucose metabolism and future risk of type 2 diabetes. Pregnancy and GDM are related to disturbed circadian rhythms and sleeping, which are determined by genetic variations in genes such as Melatonin receptor 1B (MTNR1B).Objective: We prospectively assessed whether the circadian rhythms related MTNR1B genotype was related to on 1-5 years of postpartum glycemic changes among women with a history of GDM, and whether gestational weight gain modified such associations.Design: The established circadian rhythms-associated MTNR1B genetic variant (rs10830963) was genotyped in 1025 Chinese women with a history of GDM. Body weight and glycemic traits during and after pregnancy were longitudinally collected.Results: The frequency of MTNR1B rs10830963 was not different among the three categories of gestational weight gain (inadequate, adequate, and excessive). We found women carrying different MTNR1B genotype showed distinct postpartum changes in 2-h glucose (OGTT) – 0.36, 0.20, and -0.19 mmol/L per additional copy of the G allele in women with inadequate, adequate, and excessive gestational weight gain, respectively (p for interaction=0.028). The corresponding changes in fasting glucose were 0.14, 0.13, and 0.01, though the modification effects of gestational weight gain on the genetic association was marginal (p for interaction= 0.067).Conclusions: Our findings suggest that gestational weight gain may modify the circadian rhythms related MTNR1B genetic variant on long term glycemic changes, highlighting the significance of gestational weight management in diabetes prevention among women with GDM.