Different mathematical models for a chart of intrauterine growth were tested attempting to employ uncomplicated curves. In this manner, a chart of foetal growth was elaborated by plotting the cube root of neonate weight against the gestational age. Two different regions can be clearly seen in this chart of growth. In the first one, until the 34th week of pregnancy, there is a linear relationship between the two variables. In the second region, for pregnancies above the 34th week, the curve has a quadratic equation, reaching the maximum between the 43rd and 44th week, decreasing posteriorly. The goodness of fit obtained by the present mathematical model is more satisfactory than that obtained by mathematical models with a single linear equation.