Placental growth, development, and function in relation to maternal nutrition

Maternal malnutrition in humans and also in the rat interferes with normal placental growth as reflected by a lower weight, smaller placental size, and reduced DNA content. The affected placentas also have a reduced peripheral villous mass and villous surface. Biochemical studies have revealed a reduced polysome/monosome ratio and higher levels of alkaline ribonuclease activity. However, the rate of protein synthesis in a cell free system, expressed per milligram of rRNA, is not impaired. The composition of the placenta is also altered by malnutrition. Reduced concentrations of ash, hydroxyproline, and fat have been described in human placentas and reduced glycogen and putrescine concentrations have been described in the rat placenta. The functional implications of some of these changes are still unclear. In malnourished women a reduced estriol and pregnanediol excretion have been reported. Malnourished rats near term have a reduced maternal-fetal transfer of alpha-aminoisobutyric acid and glucose, but is is still unclear to what extent the reduced transfer is due to placental factors or preplacental factors such as reduced placental blood flow, also present in malnourished animals.