The composition of the gut microbiota changes over gestation. These changes may contribute to the increase in insulin resistance that occurs in pregnancy. It is still unclear how the bacteria in the gut affect insulin resistance. Potential mechanisms include direct effects on insulin levels through stimulation of incretin hormone secretion; alterations of adipokine levels through release of bacterial metabolites or changes to the inflammatory state of the mother. In this presentation, I will explore some of these hypotheses using samples obtained from the SPRING study. In addition, I will speculate on the complicating role of diet intake, given some recent publications linking gut microbiota composition with individual responses to carbohydrates outside pregnancy.