Fetal growth restriction (FGR), formerly called intrauterine growth restriction (IUGR), refers to a condition in which an unborn baby is smaller than it should be because it is not growing at a normal rate inside the womb. Mild FGR usually doesn't cause long-term problems. In fact, most babies who have it catch up in height and weight by age 2. But severe FGR can seriously harm a baby before and after birth. The extent of the problems depends on the cause and how severe the growth restriction is. It also depends on what point in the pregnancy it starts.