Intrauterine growth retardation (IUGR) increases a risk of perinatal complications and may carry a negative influence on a later baby's mental and physical development. Poorer function revealed by many vital organs seems to be the effect of their lower mass and their relative immaturity. In the first part of a paper the authors discuss two groups of factors thought to be responsible for IUGR. The first one has been related to the fetal status-genetic anomalies, other primary developmental defects and different growth patterns.