Clinical defense response to cold and noise in preterm neonates after intrauterine conditions associated with chronic stress.

Threatening stimuli may trigger abnormal reaction patterns in animals and infants. We investigated whether chronic intrauterine stress influenced these reactions. The autonomic defense response to cold and noise in 21 preterm newborns who had suffered from chronic intrauterine stress, such as maternal smoking, maternal hypertension, and intrauterine growth retardation (STR-group) was compared with the response in 30 preterm newborns without such condition (C-group). An ice cube was applied to the forehead and a 90 dB bleeptone was presented to the ears. After the cold test the heart rate, systolic, diastolic, and mean blood pressure increased in both groups, but to a lesser extent in the STR-group: the heart rate increased more at 2 minutes in the C-group (p = 0.009), and the systolic blood pressure was higher in the C-group at 30 seconds (p = 0.007). The respiratory rate decreased in both groups. After the auditory stimulus, no significant difference in response between the two groups was seen for any of the parameters. The number of arousals between the two groups was similar for both tests; they uniformly resulted in increased heart and respiratory rates. The classic passive defense response was not observed in either group of preterm newborns. The observed reaction could be defined as a combination of a sympathetic, active fight-or-flight reaction and a parasympathetic passive freezing, or paralysis, reaction. The latter was less pronounced in the C-group. This may point to a change in the maturation of the autonomic nervous system after chronic intrauterine stress. It is speculated that this could make these infants more vulnerable in stressful situations.