Intermittent umbilical cord occlusion in the ovine fetus near term: Effects on behavioral state activity

Objective: The purpose of this study was to determine the effects on fetal behavioral state activity of intermittent umbilical cord occlusion resulting in repetitive severe short-term hypoxemia. Study Design: Fifteen near-term fetal sheep (experimental group, n = 8; control group, n = 7) were studied during 4 days while behavioral and cardiovascular parameters were monitored. Each day after a 2-hour control period, cord occlusions were performed in the experimental group animals by complete inflation of an occluder cuff (duration, 90 seconds) every 30 minutes for 3 to 5 hours. Results are presented as group mean ± SEM. Results: During umbilical cord occlusions fetal arterial PO2 (change of 12 mm Hg), oxygen saturation (change of 40%), and glucose concentration (change of 0.3 mmol/L) fell and PCO2 (change of 7 mm Hg) rose, but all returned toward control values after release of occlusion. Fetal behavioral state activity was markedly disrupted by 90 seconds of cord occlusion, with animals showing an abrupt flattening of the electrocorticogram. In >90% of instances the first identifiable state after cord release was the high-voltage non–rapid-eye-movement state. There was no apparent change in this response through the 4 days of the study. For experimental group animals the mean percentages of time spent in low-voltage electrocortical state (from 53 ± 2 to 36 ± 2), electro-ocular state (from 45 ± 3 to 28 ± 3), and fetal breathing activity (22 ± 4 to 12 ± 3) were significantly decreased (P< .001) during occlusion hours with respect to nonocclusion hours. Conclusion: Intermittent umbilical cord occlusion with severe but limited hypoxemia and no cumulative acidosis in the near-term ovine fetus disrupts behavioral state activity, with a flattening of the electrocortical activity during occlusions and an overall decrease in the prominence of the low-voltage rapid-eye-movement state. If such insults are frequent and severe enough, they might have an effect on growth and development of the brain during the perinatal period. (Am J Obstet Gynecol 1999;181:1520-9.)