Prenatal diagnosis (PND) has assistencial, psychological and economical consequences; it is very important to evaluate cost effectiveness for the population. A prospective study was done (longitudinal and descriptive) on a population referred to Maternidade Dr. Alfredo da Costa, divided into two groups. Group one with PND performed on proper time and second group a PND procedure performed on a adequate time. The general characterization, indications for reference and consequences were evaluated. The conclusions are that the indications for reference were correct and the diagnosis was effective in 17% of patients. Social, economical levels and multiparity were the most important factors affecting adequate PND. However concerning the results, the termination of pregnancy was more performed on the group 1 and more abnormalities were seen on the newborns of group 2.