Two papers selected for publication in the August 2007 issue of Biology of Reproduction demonstrate that adolescent female sheep that become pregnant before they have achieved their full growth may not be able to supply enough nourishment for their fetuses to develop without physical deficits.
These studies may also have implications for managing pregnancies of adolescent human females, who, in increasing numbers worldwide, are bearing offspring before they have finished growing.
A team of scientists, headed by Dr. Jacqueline Wallace of the Rowett Research Institute in Aberdeen, Scotland, found that limiting the food intake of adolescent ewes during pregnancy impairs the nutrient supply to their fetuses and slows the growth of soft tissue in the fetuses.
In a related finding, the team reported that a possible factor in the reduction of nutrients to the fetuses in undernourished adolescent ewes is a change in the development of blood vessels supplying nutrients to the uterus and placenta during pregnancy.
Because the changes in placental blood vessels could not be reversed by returning undernourished ewes to an optimal diet later in their pregnancy, Wallace's team pointed out the importance of adequate weight gains by pregnant teenaged girls, especially during the first two trimesters, to reduce the chance of a low-birth-weight infant.
In this study, a pregnancy was produced in each experimental ewe by implanting a single egg fertilized with the sperm of just one male sheep.
The control group of animals received an optimal diet for maintaining their pregnancies. Ewes in the experimental group were provided a diet that sustained their bodyweight at the time they became pregnant; as a result, their reserves of fat and other tissues were gradually depleted during the course of gestation.
The researchers point to evidence that competition for nutrients between a mother and her fetus "will impair nutrient supply in girls who are still growing during pregnancy. Thus formulating correct dietary advice for these young adolescent girls is likely to be complex, particularly if the mother has not completed her own growth. Our results suggest that biomarkers of growth and nutritional status at the time of conception and at mid-pregnancy, and the use of ultrasound to detect whether placental growth and function have been perturbed, may prove beneficial in the optimal management of adolescent pregnancies."