Utero-placental vascular development and placental function.

The rate of fetal growth and subsequent birth weight are major determinants of postnatal survival and growth. Because the placenta is the organ through which respiratory gases, nutrients, and wastes are transported between the maternal and fetal systems, its primary function is to supply the metabolic substrates necessary to support fetal growth. Placental growth and development, therefore, are critical for normal fetal growth and development. During the last half of gestation in mammals, growth of the fetus is exponential, whereas utero-placental growth slows or ceases. Nevertheless, unless placental transport capacity keeps pace with the continually increasing demands of the fetus, fetal growth will be compromised. Studies over the last two decades have shown that placental transport capacity does indeed keep pace with fetal growth. This increase in placental function can be accounted for primarily by continual increases in placental (uterine and umbilical) blood flows, associated with increased placental vascularity. Placental vascular growth and development, in turn, are probably regulated by angiogenic factors produced by the placental tissues themselves. These placental angiogenic factors are produced primarily by the maternal placental tissues, are heparin-binding, and seem to be related to the fibroblast growth factor family. Further elucidation of the factors responsible for placental growth and vascular development is critical for an improved understanding of uteroplacental-fetal interactions, which result in delivery of a healthy offspring.