Arginine/analogs & derivatives; Fetal Blood/metabolism; Fetal Growth Retardation/blood; Nitric Oxide Synthase Type III/metabolism; Nitric Oxide/biosynthesis; Placenta/metabolism; Adaptation, Physiological; Adult; Arginine/blood; Endothelial Cells/metabolism; Endothelium, Vascular/diagnostic imaging; Endothelium, Vascular/metabolism; Female; Fetal Growth Retardation/diagnostic imaging; Fetal Growth Retardation/genetics; Fetus; Gene Expression Profiling; Hemoglobins/metabolism; Humans; Infant, Low Birth Weight; Infant, Newborn; Nitric Oxide Synthase Type III/genetics; Nitrites/blood; Pregnancy; Reverse Transcriptase Polymerase Chain Reaction; Ultrasonography; Umbilical Arteries/diagnostic imaging; Umbilical Arteries/metabolism; Umbilical Veins/diagnostic imaging; Umbilical Veins/metabolism; Up-Regulation