Effect of hypoxia and catecholamines on the habituation rates of chronically catheterized ovine fetuses.

Integrated electromyographic, electrocortical (ECoG) and electro-ocular activity were recorded in 13 chronically prepared fetal sheep (130-145 days). Fetal movements and the rate of habituation to repeated suffusions of cold saline against the fetal skin were recorded. Experiments were repeated during an intravenous infusion of noradrenaline to the fetus (0.4 microgram/kg estimated fetal weight/min) and during hypoxia induced by altering the oxygen content of the inspired air to the ewe to 9%. Repeated stimulation with cold saline resulted in an increase in fetal movements (p = 0.009). The number of stimuli for habituation was similar in high-voltage and in low-voltage ECoG activity. The rate of fetal habituation was significantly faster during the infusion of noradrenaline compared with control measurements (p = 0.009). During hypoxia, the number of spontaneous fetal movements prior to stimulation decreased (p = 0.002). Habituation rates were also faster during hypoxemia compared with control measurements (p = 0.003). These findings may help to explain the rapid habituation rates seen in some human fetuses in at 'at risk' pregnancies.