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Preterm birth represents an acute stress for infants considering their physical immaturity and painful care procedures they are submitted to, potentially leading to altered cortisol regulation. It also represents a traumatic event for parents, sometimes leading to psychological diseases with repercussions on mother–infant relationships. Thirty preterm infants were submitted to an intervention on the mother–child relationships and were compared with 30 preterm infants without intervention and with 30 full-term infants. Salivary diurnal cortisol levels were assessed at 6 and 12 months. Diurnal cortisol levels at 6 months were lower in preterm infants without intervention as compared with other groups. At 12 months, such a difference was not found. The results of this study highlight a possible delay in the reorganization of the neuroendocrine system during the 1st year of life in preterm infants without intervention.

Previous studies have found that mothers of very preterm infants often report symptoms of posttraumatic stress, which has been related to cortisol dysregulation. However, the exact nature of this association is not clear and can be different regarding the predominance of some specific symptoms of posttraumatic stress, as suggested by a recent model. The objective of the present study is to assess the association between diurnal salivary cortisol and posttraumatic stress symptoms in mothers of very preterm infants. Seventy-four mothers of very preterm infants were included in the study. Mothers' cortisol regulation and posttraumatic stress symptoms were evaluated 12 months after child theoretical term (40 weeks of gestation). Results showed an association between higher re-experiencing symptoms and flatter cortisol slopes. These results may help to understand differences found in studies assessing the relation between severity of posttraumatic stress and cortisol levels, by supporting the symptoms' theory.

Preterm infants experience intense stress during the perinatal period because they endure painful and intense medical procedures. Repeated activation of the hypothalamic-pituitary-adrenal (HPA) axis during this period may have long-term effects on subsequent cortisol regulation. A premature delivery may also be intensely stressful for the parents, and they may develop symptoms of posttraumatic stress disorder (PTSD). Usable saliva samples were collected (4 times per day over 2 days, in the morning at awakening, at midday, in the afternoon, and in the evening before going to bed) to assess the diurnal cortisol regulation from 46 preterm infants when the infants were 12 months of corrected age (∼ 14 months after birth). Mothers reported their level of PTSD symptoms. The results showed an interaction between perinatal stress and maternal traumatic stress on the diurnal cortisol slope of preterm infants (R(2) = .32). This suggests that the HPA axis of preterm infants exposed to high perinatal stress may be more sensitive to subsequent environmental stress.

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