IUGR is a fetal disorder characterized by diminished fetal growth, especially in the third trimester. Growth retardation may be due to primary placental insufficiency or may result from a variety of maternal or fetal causes and is associated with elevated perinatal mortality and morbidity. Numerous conventional and Doppler ultrasound criteria have been proposed for diagnosing IUGR prenatally, but none on its own permits confident diagnosis of this condition. Diagnosis or exclusion of IUGR can best be achieved by the combined use of three parameters: estimated fetal weight, amniotic fluid volume, and maternal hypertension. When IUGR is suspected based on these parameters, Doppler ultrasound can help to determine the prognosis. Large fetuses, particularly those weighing more than 4,000 grams at birth, are at risk for perinatal morbidity and mortality due to obstetrical complications. These fetuses occur more frequently and are at especially high risk in diabetic mothers. The estimated fetal weight is the most direct parameter for diagnosing LGA and macrosomia and is moderately accurate with positive predictive values up to 67% in the general population and 77% in diabetics. It can be an important factor in deciding on the route of delivery in diabetic mothers.