Hormonal regulation of fetal growth.

The regulation of fetal growth is complex and poorly known. During the first trimester of pregnancy, no strict endocrine mechanisms are involved, but embryonic growth might be controlled at the level of the individual organs by supply of nutrients and by locally active growth factors. Later on, fetal growth depends essentially upon the maternoplacental cooperation in delivering nutrients to the fetus. Therefore, the major role of hormones in fetal growth is to mediate the utilization of available substrate. In late gestation, placental size and fetal growth rate are well correlated, pointing to a key role of the placenta in the regulation of fetal growth. It is therefore important to understand the molecular mechanisms involved in regulating placental development and endocrine functions. TGF alpha and EGF might play major roles as suggested by the modulation of their receptors with placental development, and by the specific alterations of EGF receptors in intrauterine growth retardation. In addition, human placenta specifically secretes placental growth hormone, the level of which is significantly decreased in the sera of pregnant women bearing a fetus with intrauterine growth retardation.