Increased vulnerability to neuronal damage after umbilical cord occlusion in fetal sheep with advancing gestation

The purpose of this study was to compare systemic responses and neurologic consequences of umbilical cord occlusion in fetal sheep with advancing gestation.

The umbilical cord was occluded for 10 minutes in nine midgestation (90 to 92 days) and 10 late-gestation (135 to 136 days) chronically instrumented fetuses. Systemic and cortical electrophysiologic effects were compared by analysis of variance. The extent of neuronal loss was determined 3 days later.

During occlusion, hypotension (23 +/- 2 mm Hg) and cortical cytotoxic edema were more marked in older fetuses (p < 0.001). On reperfusion, the edema, rebound tachycardia, and hypertension resolved within 20 minutes. Recovery of electroencephalographic activity (3.1 +/- 0.8 hours) and lactate levels (> 2 hours) was slower in late-gestation fetuses (p < 0.05). Neuronal loss, which was observed only in the older group, was predominantly in the hippocampus and was associated with the severity of hypotension during umbilical occlusion but not with systemic lactate levels.

Late-gestation fetal sheep are neurologically more susceptible to umbilical cord occlusion than are midgestation fetal sheep. Possibly the lesser ability of the older fetuses to maintain blood pressure and cerebral plasma membrane function during asphyxia contributes to the greater vulnerability in the gray matter.