Effects of prenatal nutrition upon pregnancy risk.

Abstract

A large percentage of babies born under 2500 gm are not truly premat ure especially in less privileged population. Their prognosis is different and they must be managed differently. Careful study of this phenomena of poor growth in utero shows 2 patterns of cell growth: hyperplasia is increase in cell number while hypertrophy is increase in cell size. These phases are determined by relative DNA content in the cell. Malnutrition during hyperplastic growth will retard the rate of cell division and result in an organ reduced in size and containing a reduced number of cells. This change is not reversible after the period when cell division normally stops. Malnutrition during hypertrophic gro wth prevents the increase in cell size and again results in a smaller organ but this change is reversible at any time. The cells simply fill back up with protein and the individual cells and the entire organ achieve normal size. Work on understanding the growth process is just beginning but it is apparent that homeostasis is maintained in the cell as long as sufficient amino acids and nucleotides are supplied and the synthesizing process functions. Malnutrition upsets this delicate balance at several points. It limits availability of amino acids for protein synthesis redirects nucleotides away from DNA to RNA synthesis (retarding the activity of certain enzymes and increasing the activity of others) thus giving an increased rate of degradation out of proportion to the increased rate of synthesis. This decreases protein synthesis except for certain proteins such as RNA polymerase and alkaline RNase whose synthesis is often increased. 2 types of in utero growth failure seem to occur. In placental vascular insufficiency the flow of nutrients is restricted. Animals so affected show marked reduction in liver size and cell number but only transient brain changes. In maternal protein restriction all organs are affected including the brain. If the malnutrition continues after birth brain size reduction is more than the sum of prenatal malnutrition alone added to postnatal nutrition alone. Studies of infants who died at birth or in the 1st year of life show similar types of growth failure. So far elevated RNA polymerase activity seems the most promising measure of poor fetal growth but alkaline RNase and DNA polymerase activity are under investigation.