Purpose Omentin-1 plays an important role in regulating insulin sensitivity outside pregnancy. As an adipokine derived from human placental and adipose tissue, it may be an important contributor in the biological pathway of gestational diabetes. Methods Omentin-1 was measured in a sub-cohort of 50 participants in the Omega study. We aimed to evaluate whether circulating maternal omentin-1 concentrations are associated with fasting serum glucose, insulin, HOMA-IR and maternal obesity as measured by body mass index (BMI) and subcutaneous and intra-abdominal fat thickness measurements in normoglycemic pregnant participants. We performed a subgroup analysis by BMI category. Results Omentin-1 was negatively correlated with HOMA-IR and insulin and inversely associated with serum glucose concentration in the fully adjusted model (- 47%; slope per tertile increase in concentration - 0.19; P-trend 0.01). This association was significant in non-overweight/obese (< 25 kg/m(2)) but not among overweight/obese (>= 25 kg/ m(2)) participants. The association with serum insulin was not significant in the fully adjusted model. Conclusion Circulating omentin-1 concentrations are inversely associated with serum glucose concentrations. Although the relevance of these findings remains to be elucidated, they may indicate a mechanism for the development of insulin resistance and gestational diabetes. Follow-up studies with larger sample sizes are warranted.