The role of the placenta in intrauterine growth restriction (IUGR).

Intrauterine growth restriction (IUGR) represents a reduction from the physiological growth rate. Fetal growth depends from the maternal supply of nutrients through the placenta into the umbilical circulation. Consequently, fetal growth restriction is associated with a reduced nutritional placental supply and this can result from a decrease in utero-placental blood flows as well as a reduced placental transport capacity. In IUGR, the placental supply of amino acids is significantly reduced independently from the severity of growth restriction and from the presence of hypoxia. Moreover, maternal-fetal gradients of glucose are increased in severe IUGR fetuses, i. e. those with alterations of umbilical blood flows, and reduced conversion ratios of long chain-polyunsaturated fatty acids (LC-PUFA) from their parent fatty acids have been demonstrated. Mouse and human models suggest that epigenetic regulation of fetal growth may also play a significant role, through placental imprinted genes. This review summarizes the current knowledge about placental role in intrauterine growth restriction.