Gestational diabetes mellitus (GDM) is the most common metabolic disorder during pregnancy. Women with GDM are at a high risk of developing type 2 diabetes (T2D) later in life. Moreover, uncontrolled GDM is linked with a detrimental intra-uterine environment, which leads to foetal complications and an increased risk for the child of developing obesity and metabolic disorders. The aim of the review is to examine the current knowledge and issues about the impact of dietary polyphenols on the mechanisms and/or factors regulating glucose homeostasis, inflammation and adipose tissue function in metabolic alterations linked with GDM. Moreover, this study also reviews the role of Omega-3 fatty acids in pregnancy. The study is a descriptive review based on several studies. Literature data is mainly derived from in vitro and animal models. In vitro and animal studies show that almost all subclasses of flavonoids, stilbene RSV and some olive oil phenolic compounds, interact and modulate several molecular pathways regulating insulin. Obesity worsens GDM with increased risk of developing metabolic disorders in both mother and offspring later in life. The adoption of healthy lifestyle, with adherence to a healthy dietary pattern, has positive effects on the prevention and management of diabetes.