Fetal growth restriction (FGR) is defined as a failure to achieve the endorsed growth potential. The diagnosis of fetal “smallness” is currently performed on the basis of an estimated fetal weight below a given threshold, most commonly the 10th centile. It is likely that this definition lacks sensitivity, so that it misses cases of growth restriction that do not fall below the 10th centile, but it identifies a subset of pregnancies at high risk of poorer perinatal outcome. Thus, detection of small fetuses is clinically relevant because as a whole this group of fetuses is associated with poorer perinatal outcome, and this represents opportunities for preventing cases of intrauterine fetal death, perinatal brain injury, and severe intrapartum fetal distress. In addition, evidence accumulating over the last 20 years has consistently demonstrated how being born small has important implications for the quality of health during adulthood. Population-based studies show that prenatal identification of small for gestational age (SGA) results in a reduction of adverse perinatal outcomes and stillbirth. 1 , 2 However, most SGA babies remain unnoticed until birth, even when routine third trimester ultrasound is performed. 3 , 4 Moreover, according to pregnancy audits, most instances of avoidable stillbirth are related with a failure to antenatally detect SGA. 5 However, FGR is probably among the obstetrical entities with the greatest variation in clinical management, resulting from lack of strong supportive evidence, combined with the complexity of the variables and indices for assessing fetal deterioration.