Fetal Growth Restriction refers to a fetus that has not reached its biologically expected growth potential, most often due to an underlying placental, maternal, or fetal problem limiting nutrient and oxygen supply. This is different from Small for Gestational Age, which simply describes a fetus whose estimated weight falls below the tenth percentile for its gestational age, without implying that anything is pathologically wrong. Some Small for Gestational Age babies are constitutionally small and healthy, following their genetic growth potential based on parental size and ethnicity. Fetal Growth Restriction, by contrast, indicates a deviation from the fetus’s own expected growth trajectory, often accompanied by abnormal blood flow patterns on Doppler ultrasound, reduced amniotic fluid, or other signs of compromise. Distinguishing between the two matters because Fetal Growth Restriction carries a higher risk of stillbirth, birth complications, and long-term health issues, and requires closer monitoring than a constitutionally small but healthy fetus.