The early detection of the macrosomic fetus is important to the obstetric management of pregnancies in which this growth abnormality occurs. Ultrasound has been used for this purpose but for this approach to be effective, a clear definition of macrosomia, selection of the appropriate parameters for measurement, and specification of the optimal time for carrying out the ultrasound studies are required. In this review we examine the definition of macrosomia and introduce two new terms, mechanical macrosomia and metabolic macrosomia. We also evaluate the effectiveness of the limited number of parameters studied to date and conclude that they are marginally effective, primarily because of their low sensitivity and the limitations of current ultrasound methods for estimating fetal weight. The use of the growth profile, a multiparameter approach to the evaluation of fetal growth, is suggested as a possible means for improving the effectiveness of ultrasound in detecting the macrosomic fetus.