METABOLIC AND CIRCULATORY ADAPTATIONS TO CHRONIC HYPOXIA IN THE FETUS

When oxygenation is compromised the fetus is capable of a number of ad aptive responses, both protective and potentially pathologic, which ca n be categorized as those affecting fetal metabolism and those affecti ng fetal oxygen transport, However, both the extent and the duration o f the impairment in oxygenation will bear on these adaptive responses. While fetal O-2 extraction is increased when oxygenation is acutely c ompromised thus maintaining O-2 consumption, with chronic hypoxemia th ere is a decrease in O-2 consumption paralleling that in O-2 delivery and contributed to by the resultant fall-off in growth and alterations in behavioural activity. While a redistribution of blood flow to vita l organs continues to be evident, this will be less pronounced than th at seen with acute hypoxemia reflecting diminished hormonal changes, u nderlying metabolic alterations, and the extent to which fetal blood g ases are normalized. which of this information is based on experimenta l data using unanesthetized fetal sheep with chronic catheterization; however, clinical outcome data and the use of investigative techniques including ultrasound scanning and cordocentesis have supported the re levance of this experimental data to the human situation. (C) 1998 Els evier Science Inc.