Sammanfattning/ Abstract

The life of a preterm infant admitted to a neonatal intensive care unit may be stressful from the moment of birth. Ever since Selyes’s initial characterisation of the biological stress response, cortisol has been frequently measured as an indicator of stress responsivity. However, research of the stress response in infants, especially those who are preterm and/or ill, has been scarce basically because of methodological issues.

The first aim with the thesis was to investigate the acute stress response, as measured by salivary cortisol and behaviour, for preterm infants, healthy infants, and infants at high psychosocial risk in response to certain defined handling procedures. The second aim was to investigate the stress response, as assessed by salivary cortisol and psychometric measures, for parents present during the handling procedure of their infant. The intention was to perform all investigations in an as naturally occurring situation as possible, which means that the studied procedures would have been performed irrespectively of the research.

The present thesis includes six original articles. The results of the first study demonstrate that it is feasible to collect sufficient amounts of saliva and analyse salivary cortisol in neonates using the presented method of collection and analysis. The second study shows that preterm infants, usually cared for in incubators, show no signs of discomfort and have variable cortisol responses during skin-to-skin care with their mothers. The mothers, however, experience stress and low control before their first skin-to-skin care with their preterm infant and do not relax completely until after the session. In the third study we found that preterm infants have higher baseline salivary cortisol as compared to healthy full-term infants. Moreover, preterm infants have higher and sustained pain response during a nappy change as compared to healthy full-term infants. The results of the fourth study shows that infants younger than three months, living in psychosocial high-risk families, have increased cortisol responses during a nappy change, performed by the mother. However, support, with the aim of improving mother-infant interaction, dampens the stress reaction. The results of the fifth study show that oral sweet-tasting solution in combination with a pacifier dampen the levels of the stress hormone cortisol in three months old infants during routine immunisation. Moreover, parents experience more self-rated emotional stress before immunisation if it is their first child who is being immunised. The sixth paper shows that the material used (cotton buds with wooden or plastic sticks) for saliva collection is of importance when saliva is collected but for practical reasons not centrifuged within 24 hours prior to cortisol analyse.

The present thesis shows that it is practically feasible to collect saliva and analyse the stress hormone cortisol in infants. The interpretation of infants’ and parents’ salivary cortisol responses to different handling procedures are discussed in relation to short- and long-term  consequences, neonatal intensive care, preterm birth, attachment, mood, and pain.