Fetal growth and placental function.

Fetal growth is largely determined by the availability of nutrients to the fetus. The fetus is at the end of a supply line that ensures delivery of nutrients from the maternal/uterine circulation to the fetus via the placenta. However, this supply line can not be regarded as a linear relationship. Maternal undernutrition will not only reduce global nutrient availability but will also influence the maternal and fetal somatotrophic axis. Both endocrine systems react in a very similar way to limited substrate supply. The hormones of the fetal somatotrophic axis, and in particular insulin-like growth factor (IGF)-1, are important regulators of fetal growth. Placental function is pivotal to materno-fetal nutrient and metabolite transfer. Placental function in turn, is heavily influenced by the maternal and fetal growth hormone (GH)-IGF-1 system. The placenta itself is also an active endocrine organ and it produces a large number of hormones including GH and IGF-1 as well their corresponding receptors. Thus the placenta can no longer be considered merely a passive conduit for fetal nutrition. Rather, it is actively involved in the integration of nutritional and endocrine signals from the maternal and fetal somatotrophic axes.