Habituation responses to external stimuli: is the habituation of preterm infants at a postconceptual age of 40 weeks equal to that of term infants?

OBJECTIVE

Compare the habituation responses to external stimuli between preterm infants at the postconceptual age of 40 weeks and term infants in the first days of life, and evaluate the habituation responses of the preterm infants until the age of 40 postconceptual weeks.

METHODS

Prospective cohort study of preterm infants aged <32 weeks. The habituation responses to light, rattle, bell and tactile stimuli of preterm infants were assessed at 32, 34, 36 and 38-40 postconceptual weeks. External stimuli were presented and responses were scored according to Lester and Tronik (2004). Habituation scores were compared between preterm and term infants, matched by sex, using t test. Repeated measures ANOVA was used to compare the responses between the different postconceptual gestational ages. Contrast models were used to verify the differences between the habituation responses according to the type of stimulus and the postconceptual ages.

RESULTS

51 preterm infants were studied (gestational age 29.4±2.4w; birth weight 1230±323 g). The scores for the habituation responses to the four stimuli progressively increased with advancing postconceptual age. At the age of 40 postconceptual weeks, the preterm infants were habituated to external stimuli similarly to the 51 studied term infants. The preterm infants showed higher habituation response scores for the rattle and bell stimuli than for the light and tactile stimuli.

CONCLUSIONS

Preterm infants improve their habituation responses to external stimuli as their postconceptual age increases, and, at 40 weeks of corrected age, they have similar responses to those exhibited by full-term infants in the first days of life.