Fetal growth in utero can be affected by a variety of maternal, fetal, placental, and environmental conditions. Some conditions result in low birth weight, whereas others result in macrosomia, which has different, but still significant implications. Monitoring for causative factors and signs and symptoms during pregnancy can alert the neonatal team to potential variations in fetal growth that impact the neonatal period. This chapter helps the nurse to differentiate between the different categories within the low birth weight definition. It describes the difference between intrauterine growth restriction and small for gestational age. Intrauterine growth restriction (IUGR) is an alteration in fetal growth in which the fetus's/newborn's weight is at or below the tenth percentile. The chapter helps the nurse to identify risk factors for macrosomia and details adverse events associated with post-maturity.