Transamniotic fetal feeding. II. A model of intrauterine growth retardation using the relationship of "natural runting" to uterine position.

Intrauterine growth retardation (IUGR) is a leading cause of perinatal morbidity and mortality. Most IUGR is the result of inadequate transfer of nutrients from mother to fetus. Transamniotic fetal feeding (TAFF) has been proposed as a method of treating IUGR in which nutrients, infused into the amniotic fluid, would be swallowed, absorbed, and utilized by the growth retarded fetus. To study this hypothesis, we have developed a rabbit model for IUGR and TAFF. We studied the effects of maternal nutritional deprivation, uterine artery ligation, and fetal position in the uterine horn on fetal body and organ growth in 96 rabbit litters. Nutritional deprivation (n = 28) and vascular interruption (n = 34) yielded inconsistent results with high fetal mortality. We were surprised to find that fetal growth was directly and consistently related to position in the uterine horn. There is a highly significant difference (P less than .0001) in weight between siblings in the no. 1 and no. 3 positions in the rabbit uterine horn at 30 days gestation that is not present at 23 days. This "natural" runting resembles human IUGR, which occurs during the last trimester of pregnancy and shows relative brain sparing. This model, in combination with our previously reported technique for TAFF, will make possible a controlled study of the efficacy of TAFF in the treatment of IUGR.