Effect of an Early and Intensified Nutritional Intervention on the Risk of Developing Gestational Diabetes Mellitus

The goal of this clinical trial is to learn if a nutritional intervention based on a Mediterranean diet (MedDiet), initiated early in pregnancy, reduces the incidence of gestational diabetes mellitus (GDM) and other adverse maternal, fetal and obstetric events in pregnant women considered high-risk. It will also learn about the stratification of GDM risk based on clinical, anthropometric, analytical and genetic characteristics. The main questions it aims to answer are: * Does the nutritional intervention based on MedDiet reduce the incidence of GDM in women with high risk? * How can we stratify the risk of GDM? Researchers will compare an advanced nutritional intervention based on a Mediterranean diet to standard care (general recommendations given at the beginning of pregnancy). Participants will: * Receive intensive nutritional counselling or standard regular recommendations during the first trimester of pregnancy. * Visit the clinic at the time of the first ultrasound (gestational week 8-11) and at the time of screening for GDM (gestational week 24-26). * Undergo a genetic test performed with a buccal swab.