The global incidence of preterm birth was 9.9 % in 2020, with an estimated 13.4 million newborn babies being born preterm (<37 weeks); among these, China had the fourth largest number of preterm births worldwide (Ohuma et al., 2023). Preterm infants are mostly treated in the neonatal intensive care unit (NICU) after birth because of the incomplete development of the functions of various systems and the high incidence of complications. A cohort study comprising 57 tertiary hospitals from 25 provinces throughout China reported that the survival rate of very preterm infants (<gestational age: 32 weeks) in Chinese NICUs has improved (Cao et al., 2021). The NICU experience of preterm infants affects parents’ mental health, causing various problems, such as anxiety, depression, and post-traumatic stress disorder (PTSD), and the psychological pain of the parents tends to persist after discharge (Roque et al., 2017, Schecter et al., 2020, Treyvaud, 2014, Trumello et al., 2018). A study using the Hospital Anxiety and Depression Scale investigated 100 parents in the NICU and found that 64 % and 23 % of the parents reported mild anxiety and depression symptoms, respectively (Russell et al., 2021). Approximately one in five parents reported moderate to high PTSD symptoms 1 year after their preterm infants were discharged from the NICU (Schecter et al., 2020). Concerns regarding the mental health of parents of preterm infants are growing, and proactive and effective interventions to promote parents’ mental health are urgently needed.

Many other underlying problems that should be addressed by parents of preterm infants in the NICU exist. Parents focus on their infants during NICU treatment, which inevitably affects their quality of life and sleep quality (McAndrew et al., 2019, Nordheim et al., 2016). Preterm infants experience severe illness and long hospital stays, and their parents are prone to negative psychological problems, which interrupt healthy parent–child attachment development, hinder the normal transition to parental role, and question their parenting ability, eventually leading to inferior parental care ability (Al Maghaireh et al., 2016, Ma et al., 2021, Yakobson et al., 2020). Therefore, appropriate intervention strategies should be formulated for parents of preterm infants in the NICU to improve their quality of life, sleep quality, and care ability.

Cortisol is a major hypothalamic–pituitary–adrenal axis biomarker secreted by the adrenal cortex and can be used as a hormone index to evaluate different stress modes (Bohringer et al., 2008, Corbalán-Tutau et al., 2014). The more pronounced the stress response, the higher the cortisol levels (Roos et al., 2018). Melatonin is mainly produced by the pineal gland at night, is inhibited by light, and can be detected in plasma, salivary-free melatonin, and urine melatonin metabolite, 6-sulfatoxymelatonin (6-SMT) (Ferlazzo et al., 2020). Melatonin can help adjust the body's sleep clock, maintain a natural biological rhythm, and regulate the sleep/wake cycle to improve body function (Ferlazzo et al., 2020). Based on the association of cortisol and melatonin with human stress and sleep, changes in cortisol and melatonin levels in parents of preterm infants are worth discussing.

ICU diaries are written by medical staff, family members, or friends to record the reasons for admission and daily activities of patients and supplemented by photos of patients or wards (Roulin et al., 2007). ICU diaries positively affect patients and their families (Calzari et al., 2024, Garrouste-Orgeas et al., 2012, Kredentser et al., 2018, Torres et al., 2020). Indeed, the use of ICU diaries has presented conflicting results in several reviews, and their effectiveness in promoting patients’ mental health remains uncertain (McIlroy et al., 2019, Sun et al., 2021). However, patients and families who had used the ICU diary expressed their support and recognition for the diary and that reading and writing the diary allowed for the unloading of emotions and strengthened the relationship between patients and relatives (Nielsen and Angel, 2016, Nielsen et al., 2019). The average time for nurses to write in diaries was < 6 min, indicating that ICU diaries can be considered a simple and economical nursing intervention (Nydahl et al., 2014). Most studies on ICU diaries have focused on adults and have been widely conducted in the United States of America, Denmark, England, and Sweden, while they are rarely used in pediatric intensive care units (PICUs) and NICUs (Li et al., 2022). Whether the ICU diary concept, originally designed for adult patients in the ICU, can be expanded directly to PICUs or NICUs remains to be explored. Health care providers perceive PICU diaries as beneficial to parents and healthcare teams (Sansone et al., 2023). NICU diaries showed great potential to support the parental coping process and could help parents understand the infants’ situation and act as a medium of communication between parents and infants (Willmeroth, 2023). Using the ICU diary in the NICU resulted in a reduction in parental anxiety symptoms, and most parents who applied for the NICU diary provided positive feedback (Russell et al., 2021). However, evidence from China in this regard is limited. Currently, paper diaries remain the main version of ICU diaries. With the rapid development of the Internet, networks can complete instant transmission of text and pictures, which are not restricted by time or space. Hence, we aimed to explore whether appropriate web-based ICU diaries could be used in the NICU.

In contrast to previous interventions that focused only on mothers (Chen et al., 2022, Yilmaz and Küçük Alemdar, 2021), this study included both mothers and fathers. This study aimed to examine the effects of web NICU diaries on the mental health, quality of life, sleep quality, care ability, and hormone levels of parents of preterm infants in the NICU. We hypothesized that web NICU diaries would significantly affect parents’ mental health, reducing the levels of anxiety and depression, as well as the prevalence of PTSD, when compared with the group that received routine care only. We also hypothesized that web NICU diaries would demonstrate greater improvements in parents’ quality of life, sleep quality, care ability, and cortisol and melatonin levels.