INCREASED VULNERABILITY TO NEURONAL DAMAGE AFTER UMBILICAL-CORD OCCLUSION IN FETAL SHEEP WITH ADVANCING GESTATION

OBJECTIVE: The purpose of this study was to compare systemic responses and neurologic consequences of umbilical cord occlusion in fetal shee p with advancing gestation. STUDY DESIGN: The umbilical cord was occlu ded for 10 minutes in nine midgestation (90 to 92 days) and 10 late-ge station (135 to 136 days) chronically instrumented fetuses. Systemic a nd cortical electrophysiologic effects were compared by analysis of va riance. The extent of neuronal loss was determined 3 days later. RESUL TS: During occlusion, hypotension (23 +/- 2 mm Hg) and cortical cytoto xic edema were more marked in older fetuses (p < 0.001). On reperfusio n, the edema, rebound tachycardia, and hypertension resolved within 20 minutes. Recovery of electroencephalographic activity (3.1 +/- 0.8 ho urs) and lactate levels (> 2 hours) was slower in late-gestation fetus es (p < 0.05). Neuronal loss, which was observed only in the older gro up, was predominantly in the hippocampus and was associated with the s everity of hypotension during umbilical occlusion but not with systemi c lactate levels. CONCLUSION: Late-gestation fetal sheep are neurologi cally more susceptible to umbilical cord occlusion than are midgestati on fetal sheep. Possibly the lesser ability of the older fetuses to ma intain blood pressure and cerebral plasma membrane function during asp hyxia contributes to the greater vulnerability in the gray matter.