Placental insufficiency is a complication of pregnancy in which the placenta cannot carry enough oxygen and nutrients to the growing fetus. Placental insufficiency may be caused by impairment in the maternal circulation, fetal circulation or both by vascular thrombosis. The placenta is the key organ integrating maternal nutritional, metabolic, endocrine and vascular conditions and fetal requirements. Fetal nutritional requirements may not be met in conditions that alter placental function, as the availability of oxygen and nutrients to the fetus depends on the interplay between placental transporters and metabolic activity. Placental transport of amino acids is an active transport with fetal concentrations higher than the maternal. The temporal sequence of abnormal Doppler changes in the fetal circulation has been described in severe intrauterine growth restriction (IUGR). Placental insufficiency is associated with a specific placental and fetal phenotype, with progressive levels of compromise leading to organ failure.