Ecologic physiology of the fetus. Ultrasonography of supply-line deprivation syndromes.

Supply-line deprivation is a major source of developmental fetal pathology. Clinical surveys have tended to emphasize the role of placental failure, although the umbilical cord may also be a site of injury. Supply-line limitations are met by a series of active fetal compensatory maneuvers. These include growth retardation. The role of ultrasound is in detecting when these compensations are invoked, grading their effectiveness, and determining trends. Nuchal cord occurs in about a third of cases, conferring a risk of hypoxic injury in utero but also providing a unique physiologic test possibility. Clinical evaluation and management should be predicated upon pathophysiologic considerations, with examination technique and extent individualized for each case.