Effects of intrauterine nutritional supplementation on fetal growth retardation.

The effects of fetal nutritional supplementation on experimentally induced growth retardation were investigated in third-trimester sheep. The control group, C, was fed ad libitum (n = 8). Group R received a protein- and calorie-restricted diet over the last 3 weeks of gestation (n = 8). Group RS was given the same restricted diet as group R, and fetal, intragastric supplements of amino acids and glucose (n = 7). Over the experimental period, maternal weight increased 4.1 +/- 0.6 kg in C but was stable in R and RS (p less than 0.01). R and RS ewes and fetuses showed biochemical evidence of malnutrition but the changes were less severe in the RS group (p less than 0.05). Nutrient levels did not change in group C ewes and fetuses. At delivery, R lambs were smaller in weight and length than RS or C (p less than 0.05); gestational ages were the same. Weights were: R, 2,702 +/- 182 g; RS, 3,235 +/- 121 g; and C, 3,290 +/- 297 g. R also had lower fetal to maternal weight ratios and higher brain to body weight ratios than RS or C (p less than or equal to 0.05). Placental size was reduced 28% in R compared to C (p less than 0.05) and was intermediate in RS. The disparity in fetal size was explained by differences in nutrient acquisition between groups. Over the experimental period, caloric intake rose 24% in C fetuses; near delivery, they had the highest umbilical uptakes of carbohydrate and alpha-amino nitrogen. After maternal diet was limited, R and RS fetuses had dramatic decreases in umbilical uptake of alpha-amino nitrogen and static umbilical uptakes of carbohydrate. Caloric intake fell 42% in R. RS fetuses, however, were receiving sufficient gastric supplementation so that umbilical + gastrointestinal carbohydrate uptake equalled that of controls, and entry of alpha-amino nitrogen and calories was intermediate, between those of R and C. Fetal oxygen consumption reflected the differences in nutrient uptake, being greatest in C, lowest in R and intermediate in RS. Fetal supplementation lessened the drain on maternal nutrients and promoted more normal fetal growth and metabolism.