Recently, more and more researchers have been using salivary cortisol reactivity to evaluate stress in preterm infants in the neonatal intensive care unit (NICU). The aim of this integrative literature review was to summarize the evidence of interventions leading to a change in salivary cortisol from the baseline in preterm infants in the NICU. The electronic databases of PubMed, CINAHL, Web of Science, and Scopus were searched for relevant studies. The inclusion criteria were studies with preterm infants exposed to an intervention evaluated by salivary cortisol reactivity before discharge from the NICU, which were published in English. In total, 16 studies were included. Eye-screening examination and heel lance provoked an increase in the salivary cortisol level. Music, prone position, and co-bedding among twins decreased the salivary cortisol level. Several studies reported a low rate of successful saliva sampling or did not use control groups. Future studies need to focus on non-painful interventions in order to learn more about salivary cortisol regulation in preterm infants. Moreover, these studies should use study designs comprising homogenous gestational and postnatal age groups, control groups, and reliable analysis methods that are able to detect cortisol in small amounts of saliva.
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