maternal – deficient supply of nutrients: smoking, malnutrition, multiple gestations, anemia, high altitude, maternal vascular disease, severe diabetes
placental – extensive placental infarctions, chronic partial separation, placenta previa
fetal – decreased intrinsic growth, congenital heart disease, genitourinary anomalies, CNS anomalies, chromosomal abnormalities (trisomy 13, 18, 21), viral infection (rubella, CMV)
symmetric = severe, early onset, fetal causes such as chromosomal abnormalities