Hello, IUGR or intrauterine growth retardation is caused by several factors, some of them being malnutrition, diabetes, hypertension, anemia, heart disease, infections like syphilis, rubella or toxoplasmosis, lung disease, kidney infection, chromosomal defects in the fetus, smoking and alcohol abuse. The fetal measurements show deviation from the normal. Though, a margin of 2 weeks + or - can be allowed, beyond this, it should be considered a deviation. A repeat sonogram after a week or two should further clarify the situation. Hope this helps.