Objectives: to identify trendand factors associated with adverse birth weight. Methods: cross-sectional design. The analysis uses the 2009-2015 Uruguay Perinatal Computer Systemdata on 303,625 newborns. Results: the prevalence of macrosomia (> 3,999g) has increased from 7.0% to 8.4%. The prevalence of low birth weight (LBW) (< 2,500g) decreased, standing at 6.6% in the last year. The factors that determines more possibilities of LBW were preeclampsia (OR = 4.80; CI95%= 4.57-5.05), inadequate

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... trols (OR = 2.29; CI95%= 2.20-2.39), shorter duration of pregnancy (OR = 2.52; CI95%= 2.50-2.55), previous hypertension (OR = 2.11; CI95%= 1.96-2.27), hypertensive disease of pregnancy (OR = 1.82; CI95%= 1.74-1.90), low prematernal maternal weight (OR = 1.65; CI95%= 1.58-1.74). Macrosomia was associated with type 1 diabetes (OR = 2.21; CI95%= 1.86-2.61), Type 2 or Gestational (OR = 1.78; CI95%= 1.70-1.87), obesity maternal (OR = 2.33; CI95%= 2.24-2.43) and longer gestation duration (OR = 2.62; CI95%= 2.53-2.72). Conclusions: the LBW decreases while the macrosomia increases. The health and nutritional status of women at the beginning of pregnancy, pathologies of the last trimester, smoking, shorter duration of pregnancy and inadequate controls are associated with BPN. Overweight, obesity and metabolic diseases determine macrosomia.