Gestational diabetes mellitus (GDM) is an increasing public health concern that affects approximately 5-20% of pregnancies with rising prevalence. The potential impact of specific dietary interventions on the gut bacteria composition and function are of considerable interest to prevent and treat GDM. The aim of the study was to analyse the changes in the gut microbiota and the diet-microbiota interactions occurring during healthy pregnancies and pregnancies complicated by GDM. This study is a systemic review. Literature shows that pregnancies complicated with GDM may have an impaired gut microbiota, and this microbiota can be transmitted to the offspring. Diets can shape the gut microbiota, in fact dietary changes can rapidly change the gut microbiota. However, it generally reverts to the original status with short-term dietary modifications. Authors conclude that the optimal nutritional strategy in GDM patients remains unresolved. It is important that the potential benefits of diet are taken into consideration.