Brain-sparing Circulation in Growth-restricted Human Fetuses

Abstract: The aim of the studies was to explore fetal circulatory changes relative to development of brain-sparing flow (BSF) in growth-restricted fetuses exposed to acute hypoxic stress, as provoked by uterine contractions during an oxytocin challenge test (OCT).(1) In fetuses with a normal cerebral circulation during basal conditions, signs of an acute hyperperfusion in both the arterial and venous cerebral vascular systems were demonstrated in response to acute hypoxic stress; (2) Fetuses with an already established BSF showed no further ability of brain-sparing during acute hypoxic stress; (3) In venous cerebral vessels of fetuses with established BSF, the flow responses to hypoxic stress were equivocal, indicating different reactions in areas drained by different veins, or a deranged physiological vascular response; (4) Blood flow changes occurred synchronized in the middle and anterior cerebral arteries when fetuses with an intact cerebral circulation were exposed to hypoxic stress; (5) When fetuses with an established BSF showed no further changes in the middle cerebral artery, no changes were found in the anterior cerebral artery either. Hence, there was no evidence of an intracerebral regional redistribution of flow during acute hypoxic stress; (6) Two mechanisms for development of acute BSF were indicated: one while the umbilical artery vascular flow resistance increased and one while it decreased. In the former situation no flow velocity changes were found in ductus venosus with development of BSF, suggesting the fetal circulation is centralized at the expense of the umbilicoplacental circulation; In the latter situation, the ductus venosus diastolic flow velocity increased and the ductus? vascular resistance decreased in a serial relationship with development of BSF; (7) The rate of positive (abnormal) OCT increased, and the chance of vaginal delivery decreased, with severity of both fetal growth restriction and umbilical artery blood flow changes; Due to only a 7-8 % chance of vaginal delivery, women with severe fetal growth restriction and/or severe blood flow changes are recommended delivery by elective cesarean section; (8) Fetal BSF is a poor predictor of a positive OCT, and of cesarean section in OCT negative women (Cohen's Kappa coefficients ? 0.23).