Introduction: in Chile as well as in most of the world, obesity and related chronic diseases (cardiovascular diseases, cancer and diabetes (NCDs)) are presently the main causes of death and disability. Although these conditions are observed mostly in adulthood, there is now considerable evidence that indicates that they are rooted in the first 1000 days of life (from -1 to + 2yrs of life).

Several studies show that maternal BMI before conception and during pregnancy predict future risk of obesity and associated metabolic conditions for both mother and offspring. Weight gain during the first two years of life is also critical, not only to ensure infant survival, but also in defining the infant's predisposition to the emergence of chronic diseases during adulthood. From a population perspective, the most effective approach to counteract the epidemic of obesity and NCDs is to prevent them. Recommendations for healthy diets and physical activity during pregnancy and infancy, as well as monitoring of nutrition goals are currently available in the Chilean primary health care system. However, most of these recommendations are not up to date and virtually all are poorly implemented. Objective: to assess the effectiveness of delivering (via primary health centers) an intervention that enhances compliance with up to date nutrition and health care standards (regarding diet, physical activity and breastfeeding promotion) during pregnancy and the first year of life. The main goal is that mothers achieve adequate nutritional status \& metabolic control, during and early after pregnancy, and that infants grow and develop healthily (adequate linear and ponderal growth according to WHO standard, while avoiding excess BMI gains) Methods: this is a cluster randomized controlled trial (CRCT), designed as a public health "program effectiveness" study (i.e. intervention will be available through the established national health system under standard operating conditions). The cluster units will be 12 primary health care centers (PHCC) in South-East Santiago randomly allocated to: 1) enhanced nutrition and health care standards (intervention group) or 2) routine care (control group).

Women seeking care before 15 weeks of pregnancy, residents within a catchment area of selected PHCCs, who are not planning to move in the next two years will be invited to participate in the study. Pregnant women classified as high risk according to the norms of the Chilean Ministry of Health (MoH)and/or underweight (BMI\<18.5) will be excluded. We will recruit 200 women in each PHCC and assuming a 20% loss to f-up we will end with 960 women per arm of the study. After randomization, pregnant women in the intervention PHCCs starting at their first pre-natal visit (\< 15 wks.) will receive, diet and physical activity (PA) counseling-support based on updated recommendations and monitoring goals for weight gain \& glycemic control and breastfeeding (BF) promotion till 12 months postpartum. Pregnant women who attend control PHCCs will receive routine antenatal care according to national guidelines. The outcomes will be: 1)achievement of adequate nutritional status \& metabolic control during pregnancy: a. Weight gain according to Institute of Medicine (IOM) recommendations, b. glycemic control based on ADA 2011 recommendations, 3. No weight retention at 12 months, and 2) healthy infant growth and development: a) height and BMI growth based on WHO standards, b) normal abbreviated psychomotor development test (TEPSI) and evaluation scale of psychomotor development (EEDP) at 12 months. Mothers \& infants will be monitored to ensure the safety of the intervention (assessment of undernutrition, micronutrient deficiency and indices of poor nutrition). Data will be collected as part of routine health care activities and analyzed based on the allocation to each study group ("intention to treat"). Results will be presented as appropriate effect sizes with a measure of precision (95% confidence intervals). Further exploratory analyses will be based on those participants that fully follow the protocol ("per-protocol analyses"). Expected results: we expect that the intervention will benefit the participants in achieving adequate nutritional status \& metabolic control, during and early after, pregnancy as well as adequate infant growth \& development as a result of an increase in the impact of standard nutrition and health care practices. The results should be potentially extended to the rest of the primary health care system given the "program effectiveness" approach that will be taken. Additionally, we expect that this study will serve as a core project in which other ancillary projects will be nested. Gathered information should contribute to a better understanding of how to develop effective interventions to halt the maternal and obesity epidemic and its associated co-morbidities in the Chilean population.