Introduction: birth weight is a determinant factor in the health of newborns. Factors related to health and maternal behaviors influence the birth conditions and, consequently, birth weight. Objectives: to determine the relationship between maternal characteristics and birth weight. Patients and methods: this was a longitudinal study performed in two stages including 87 women. In the first, pregnant women answered a questionnaire with socioeconomic information, variables related to pregnancy, obstetric history, and 24 hours food recall. The second stage took place in the first postpartum month; nursing mothers were questioned through telephone contacts about their delivery characteristics, their newborn, and total weight gain during pregnancy. Logistic regression analysis was used to analyze the relationship between the pregnancy variables and birth weight. Results: the average consumption of iron, calcium, folic acid, and vitamin A were below the nutritional recommendations, except for vitamin C, which was appropriately consumed. After the logistic regression adjustments, the variables pre-pregnancy nutritional status (OR = 5.457; p = 0.012), start of prenatal care (OR = 1.509; p = 0.015), and density of dietary calcium (OR = 2.672; p = 0.048) remained associated with birth weight. Conclusions: the importance of medical and nutritional appropriate follow-up during the prenatal period is highlighted in order to minimize the occurrence of adverse effects on pregnancy and damage in the health status of newborns.