Currently no evidence from randomized clinical trials on the efficacy of treatment of gestational diabetes mellitus (GDM), diagnosed by a single altered value during a 75g oral glucose tolerance test (75g OGTT), proposed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) to reduce adverse perinatal outcomes (APO). In our institution GDM diagnosis is established with two or more altered values during 75g OGTT, women with one altered value during OGTT are not considered GDM and therefore those women do not receive specific treatment for GDM. We conduct an open randomized clinical trial, two groups, Group 1 (women with treatment for GDM) and group 2 (women with routine care). The diagnosis of GDM will be perform with a single altered value during 75g OGTT: fasting ≥ 92mg / dL, 1-hour ≥ 180 mg / dL and 2-hours ≥ 153 mg / dL. Treatment consist of medical nutritional therapy (MNT), which includes restricted diet 45% carbohydrate, exercise and self-monitoring of glucose, if not reach therapeutic goals metformin and / or insulin will be added.