Nutritional Characteristics of Amniotic Fluid

Abstract

After completing this article, readers should be able to: 1. Explain the role of amniotic fluid in fetal nutrition and neonatal health. 2. Define the most important macro- and micronutrients in amniotic fluid. 3. Describe the important growth factors contained in amniotic fluid. 4. 4Discuss the current and future directions for research in amniotic fluid-related fetal nutrition and neonatal health. Amniotic fluid (AF) is an accepted physical barrier against fetal trauma and a defense against fetal infection. The importance of AF in fetal nutrition also is an acknowledged fact. Fetal malnutrition related to abnormalities of AF and its consequences on neonatal health, however, are not fully appreciated. This review examines the nutritional characteristics of AF. In 1975, fetal swallowing was shown to be the primary method of clearing proteins from AF. ( 1) Using near-term Rhesus monkeys and 35S-labeled proteins injected into AF, 10% to 15% of nitrogen accretion in late pregnancy was shown to be related to fetal swallowing. A decade later, Mulvihill and colleagues ( 2) reported experiments that ligated the esophagi of fetal rabbits to prevent swallowing of AF. These researchers subsequently infused different nutritive solutions into the fetal stomach and compared growth and organ weights. Swallowing of AF enhanced fetal gastrointestinal development, and in late gestation, accounted for 10% to 14% of the nutritional requirements of the normal fetus. In sheep, esophageal ligation causes abnormal enterocyte differentiation and decreases fetal intestinal growth, conditions that are mitigated by re-establishing fetal swallowing. ( 3) Ultrasonography recently defined gastric emptying cycles in human fetuses throughout pregnancy, and near-term, the delay in gastric emptying may be related to satiation. ( 4) The effect of AF on fetal intestinal and somatic growth in humans is more circumstantial (Table 1). In 1994, Surana and Puri ( 5) studied jejunal versus ileal atresia and discovered …