PURPOSE To characterize prenatal care and to evaluate the association of its adequacy with maternal, socioeconomic and environmental sanitation characteristics, as well as the influence of these factors on the birth weight of the children. METHODS The eligible population for the study consisted of all women who had children during 2009 and lived in the city of Queimadas at the time of data collection. Information was collected with a questionnaire applied to the mothers in Family Health Basic Units or in their residence. The prenatal care adequacy index (outcome variable) was defined as adequate when the mother attended six or more prenatal visits and began monitoring during the first trimester of pregnancy (<20 weeks). Hierarchical logistic regression was performed to estimate the odds ratios for inadequate prenatal care and a multiple linear regression model was used to estimate the effect of adequacy of prenatal care and maternal, socioeconomic and environmental sanitation variables on birth weight. The statistical program used was Rv2.10.0, with the level of significance set at p <5%. RESULTS Of a total of 199 women studied, 78.4% were classified as having received adequate prenatal care. After adjustment for other predictors, maternal age of 19 years or less remained as an explanatory variable of inadequate prenatal care (OR 4.27, 95%CI 1.10 - 15.89). Even after controlling for variables, child's birth weight was negatively associated with water supply from a well/spring and burnt/buried garbage, accounting for weight reductions of the order of 563.8, 262.0 and 951.9 g, respectively. CONCLUSION Adequate prenatal care can alleviate the influence of socioeconomic disparities related to health care. Even in this situation, teenage mothers are more likely to receive inadequate prenatal care and low birth weight is favored by improper sanitation conditions (such as water supply and garbage disposal).