During the past 15-20 years, ultrasonic estimation of fetal weight (EFW) has been used increasingly to make management decisions regarding the induction of labor or delivery route. The propriety of this approach depends on proof that its use improves newborn or maternal outcome without disproportionate increases in morbidity and mortality. A barrier to achieving this goal is the inaccuracy associated with ultrasonic EFW. The current ultrasonic EFW procedures are not' accurate enough for detecting macrosomia defined by weight criteria. Even if clinicians could determine fetal weight accurately, the frequency of persistent fetal injuries associated with vaginal birth of the macrosomic fetus is so low that induction of labor or cesarean birth is not justified on that basis. Furthermore, the inaccurate ultrasonic determination of fetal weight leads to inappropriate obstetric interventions. Evidence-based decisionmaking should be an important goal for all obstetric care givers. Delivery decisions based on inaccurate EFW should be avoided.