title: Pain reactivity in preterm neonates: examining the sex differences.
abstract: BACKGROUND
  Early and repeated experiences of pain may have long-term effects on vulnerable newborns hospitalized in the Neonatal Intensive Care Unit (NICU), and neonatal pain responses may be affected by a variety of factors that neonates encounter. We tested the hypothesis that male preterm neonates exhibited greater pain sensitivity than females by assessing biobehavioural pain reactivity and recovery patterns to painful procedure.
  
  
  METHODS
  Fifty-three infants born preterm and low birthweight who were admitted to NICU were observed during five phases (baseline, antisepsis, puncture, recovery-dressing and recovery-resting). Behavioural pain reactivity was measured using the Neonatal Facial Coding System (NFCS) and the Sleep-Wake States Scale (SWS). The heart rate (HR) was continuously recorded. All measures were assessed based on scores and magnitude of responses.
  
  
  RESULTS
  We found that male and female preterm neonates had similar patterns of behavioural pain reactivity and recovery; there were no statistical differences between groups in NFCS and SWS scores. However, male preterm infants presented higher HR immediately in the first minute of the puncture phase and also higher change in maximum HR between the baseline and puncture phases, than female preterm infants.
  
  
  CONCLUSIONS
  Although we found that male infants showed higher physiological reactivity to painful stimulus in some HR parameters than female infants, the evidences were not sufficient to confirm the influence of sex on biobehavioural response to pain in vulnerable neonates.
authors.affiliation: Department of Neuroscience and Behavior, Ribeirão Preto Medical School, University of São Paulo, Brazil.
authors.forename: B O
authors.initials: BO
authors.lastname: Valeri
authors.forename: C M
authors.initials: CM
authors.lastname: Gaspardo
authors.forename: F E
authors.initials: FE
authors.lastname: Martinez
authors.forename: M B M
authors.initials: MB
authors.lastname: Linhares
mesh_terms: D015331:Cohort Studies; D005149:Facial Expression; D005260:Female; D006339:Heart Rate; D006801:Humans; D018730:Infant Behavior / Q000502:physiology*; D007231:Infant, Newborn; D007234:Infant, Premature / Q000502:physiology*; D019102:Infant, Very Low Birth Weight; D008297:Male; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D011446:Prospective Studies; D012737:Sex Factors; D012890:Sleep; D013312:Stress, Physiological / Q000502:physiology*