This is a Systematic Literature Review (SLR). For its operationalization, the recommendations of the Cochrane Institute seven steps for carrying out SLR were followed, namely: 1) Formulation of the question, 2) Location and selection of studies 3) Critical evaluation of studies 4) Data collection, 5) Data analysis and presentation, 6) Data interpretation, and (7) Review improvement and update (Higgins & Green, 2011). It drew also from the criteria adopted by the PRISMA recommendation, which consists of a checklist with 27 items. The PRISMA criteria directed to meta-analyses were not used.

The first step consisted of formulating the question; for this purpose, the PVO technique was used, which consists of an adaptation of the PICO model, aimed at research dealing with issues associated with psychology or related areas (Biruel & Pinto, 2011). Based on the application of this technique, it is considered: (a) Q (question): Which variables are associated with parental stress of premature babies’ parents?; (b) V (variables): those associated with parental stress of preterm infants’ parents; and (c) O (outcomes): identify, describe and review the variables associated with parental stress in preterm infants’ parents.

As for the second step, location and selection of studies, the search strategy consisted of using the following Boolean descriptors and operators: (Parental stress OR Maternal stress OR Paternal stress) AND (Preterm OR Preterm infant OR Premature infant). The inclusion criteria were: (a) empirical articles available in full and free of charge; (b) in English and Portuguese; (c) published from January 2009 to December 2020 (d) target audience: parents of premature babies (mother, father or both); (e) specific instruments used to assess parental stress; and (f) peer-reviewed articles. Articles of SLR, essays, reviews, not available in full for free, published in other languages, that did not assess parental stress and those published before or after the indicated dates in the inclusion criteria were excluded. The following databases were consulted: CINAHL, Cochrane Library, Medline, PsycInfo and Web of Science that contain different types of information in health and other areas with independent and high-quality evidence for decision making.

The third and fourth stages consisted of the critical evaluation of the studies and data collection. The selected articles were submitted to tests to verify the methodological quality. The relevance test I, applied to titles and abstracts by the main researcher, consisted of two objective questions. Subsequently, the relevance test II was applied by two independent judges, who read the full articles; the test consisted of five objective questions. When there was disagreement between the reviewers, a third judge was consulted.

Data collection followed the following steps: data mining to characterize the articles, which were organized in a Microsoft Excel 2015 software spreadsheet. After data collection, studies that, in addition to investigating parental stress, also evaluated other psychological symptoms, such as anxiety, depression, post-traumatic stress, among others, were selected to enter this review. Therefore, the objective and method of the selected articles were analyzed. Subsequently, the objectives of the studies that met this prerogative were transcribed and the main variables investigated were cut out.

In the fifth stage, the analysis and presentation of the data took place. With the objectives that make up the database, terms with the same semantic value and representing the same idea were organized. Subsequently, the analysis was carried out using the NodeXL Program (version 1.0.1.251), which allows calculating metrics to identify dynamic interactions, intermediation rules and degrees of centrality between the elements that make up the set of variables of interest to researchers (Hansen et al., 2010; Ramos et al., 2020).

Among the metrics, the following deserve to be highlighted in this study: 1) Eigenvector Centrality, which measures the links between neighboring vertices, to verify which links pass through a given vertex. Thus, the more edges a pair of vertices receives, the stronger the connection between them (Pinheiro, 2013; Ramos et al., 2020); 2) Clustering Coefficient C(C), which measures the tendency of the vertices in a network to cluster, forming clusters, taking as a starting point the existing triads in the network, that is, it is a metric generated by the measure of relative value of triangles existing in the graph. The larger the C(C) of a graph, the shorter the paths between its vertices (Pinheiro, 2013; Ramos et al., 2020). Finally, in the sixth and seventh stages, data interpretation and the improvement and updating of the review took place.

A total of 655 articles were identified in the databases, including CINAHL (113), Cochrane Library (161), Medline (180), PsycInfo (67) and Web of Science (134). The relevance test I was applied to 180 articles and the relevance test II was applied to 58 articles that were read in full by two independent judges. In addition to assessing parental stress, studies that investigated other psychological symptoms (such as anxiety, depression, post-traumatic stress) associated with parental stress were selected. Only 12 articles met this criterion and are the ones that make up the sample of this SLR. The four steps that make up the PRISMA flowchart and that were followed in data collection can be seen in Figure 1.

As for the characterization data, it was observed that 50% of the articles reviewed were issued in the United States (6), 17% of the articles are from Italy (2), and the other articles are from Australia (1), Greece (1), Canada (1) and New Zealand (1); each of these four countries represents 8% of the sample, totaling 32%. Regarding the year of publication, in 2014 five articles were published, and this was the year with the highest number of articles (41.67%), followed by the years 2015 and 2016, in which two articles were published each year, which represents (33.34%). Regarding the participants, 58.33% had the participation of only the mothers; father and mother participated in 41.67% of the surveys (Table 1).

Through the multigraph analysis (Figure 2) it was observed that not all vertices had the same importance in the network. A vertex is considered central if it has many links (Fonseca-Pedrero, 2017). In this connection, regarding the psychological distress of parents’ vertex, the most influential in the multigraph, the literature has shown that, in addition to high levels of stress, parents of premature/low birth weight babies have high levels of depression, anxiety and post-traumatic stress when compared to parents of full-term babies (Bener, 2013; Gangi et al., 2013; Ong et al., 2018). Along this line, the study by Coletti et al. (2015) indicated that mothers of very preterm infants (gestational age ≤ 32 weeks) had significantly higher levels of stress than mothers of late preterm infants (gestational age 33-36 weeks); these mothers are likely to face more difficulties in the daily management of the child and his/her demands.

Regarding the parent-infant relationship vertex, which also occupied a central position, the literature has shown that the parents’ relationship with the premature baby is influenced by variables such as child characteristics, parents’ psychological distress, risk factors and intervention. The study by Gangi et al. (2013) revealed that early involvement of parents, and especially of mothers, in neonatal care (particularly if the initial assessment indicates a high risk of anxiety), besides the familiarization with the NICU setting should constitute a primary objective to prevent the occurrence of a post-traumatic stress disorder. Such findings demonstrate the relationship between the vertices parent-infant relationship and parents’ psychological distress. The long stay of the premature infant in the NICU changes the role of parents, since care is now carried out, above all, by the multidisciplinary team, which can generate a feeling of incapacity in parents, and be associated with increased psychological distress (Contim et al., 2017; Ong et al., 2018).

Studies on the risk factors, the third most important vertex in the multigraph, indicate that mothers of babies with very low birth weight, high risk and who were in conditions of low social support had higher levels of personal, family and child-related stress when compared to mothers of full-term babies (Singer et al., 2010). Babies born prematurely, who have more risk factors and clinical comorbidities, are those who may generate more distress in their parents, which occurs as a result of fear and concern about unfavorable outcomes (Contim et al., 2017; Ong et al., 2018).

As to the relationship between the vertex environmental characteristics and parents’ psychological distress, the results of the study by Pisoni et al. (2019) draw attention, as mothers of premature babies admitted to the NICU reported intense symptoms of postpartum depression and a high level of stress, even though their children had low perinatal risk and normal neurological exams.

The maternal characteristics and child characteristics vertices are peripheral vertices, that is, they are at the end of the network and make few connections. Divergent data were observed in the literature, such as the relationship between the age of preterm infants’ parents and levels of parental stress and other psychological symptoms. In the study by Gondwe et al. (2017) parental stress, depression, and worry scores were higher in mothers in the higher age groups. On the other hand, Bener (2013) identified that mothers of premature babies and who had higher depression and anxiety scores were the youngest, least educated, in addition to the baby having lower body weight and the family having lower income. Such data are corroborated by other studies that claim that both young mothers and fathers, especially adolescents, experience greater levels of psychological distress for having a premature child. It is possible that this datum is due to parental figures not knowing how to act and what to expect from the situation (Dudek-Shriber, 2004).

Although 41.67% of the sample of this SLR articles participants is composed of mothers and fathers of premature babies, it is noteworthy that the vertex originated refers only to “Maternal characteristics”, that is, no vertices referring to paternal characteristics were found. Despite the authors’ efforts to include the father figure in the research, the data and discussions are mostly aimed at mothers, who are the main parental figures who take care of the child. This reality has been progressively undergoing transformations. Ordinance 930, of May 10, 2012, of the Ministry of Health, which defines guidelines on comprehensive and humanized care for serious and potentially serious premature infant, determines that mothers and fathers have free access to NICUs; in addition, the participation and protagonism of the mother and father in the care of the premature infant should be encouraged (Ministério da Saúde, 2012).

In order to reduce parental stress, there must be adequate social support. Thus, the literature indicates that higher levels of parental stress would be negatively associated with the quality of fatherhood and co-parenting, that is, with less support from the father figure in child care (Lucassen et al., 2021; Stevenson et al., 2019).

The authors note the enhancement of male participation in domestic activities. However, the tasks of caring for the children continue to be carried out mostly by the mothers. As explanatory hypotheses, it is pointed out that paternity would be culturally more sensitive to contextual influences, such as stress and demands from the work environment, which can result in the use of more coercive parenting strategies and less effective co-parenting strategies. In contrast, cultural patterns and the potency of the mother-child dyad can make mothers more likely to remain in their parental roles, regardless of the demands of the environment (Lucassen et al., 2021; Stevenson et al., 2019).

From this perspective, the susceptibility that single-parent families have to parental stress should be considered. The study by Stack and Meredith (2018) explored the impact of financial difficulties on the well-being of single mothers. The results showed high levels of stress, psychological distress and anxiety, including rumination of thoughts, insomnia and suicidal ideation, which were associated with an overload in the parental role, and a decrease in social support or coparenting. Thus, high levels of stress and lack of support can lead to ineffective coping strategies, which highlights the need to share parental roles and the benefits that single mothers can have with interventions, since there is a greater tendency for this group to experience overload feelings.

Regarding the child’s characteristics’ vertex, the baby’s age does not seem to be a significant predictor of stress, since even after hospital discharge, their mothers’ stress levels did not change significantly over time, remaining high in the first years of the child’s life. In addition, these babies have some prevalent characteristics, such as more frequent crying episodes, reduced parental interaction, babies who do not meet expectations (such as physical or emotional characteristics) compared to full-term babies, and tend to be perceived by mothers as more vulnerable and at greater risk of developing comorbidities (Mughal et al., 2017), which could lead to a situation of continuous stress for mothers (Spinelli et al., 2013).

As for the intervention vertex, the literature has shown that the implementation of programs for the family, through early educational and emotional support aimed at parents of premature babies, in addition to identifying the exact sources of parental stress on an individual basis, seem to reduce stress in the NICU environment (Schappin et al., 2013; Ong et al., 2018).

Through network analysis, we could extract the pattern of the awareness network involving the theme of prematurity and parental stress. In this connection, the present review contributes with the literature by identifying the most central vertices in the reviewed studies, namely: psychological distress of parents, parent-infant relationship, risk factors and environmental characteristics.

Despite its contribution, this SLR has some limitations, such as the non-inclusion of articles published in other languages. In this connection, it is recommended that future studies be more comprehensive, including search terms such as “anxiety”, “depression” and “posttraumatic stress”. It is suggested that SLR studies be developed that use the technique of analysis and visualization of graph data, identifying the most strongly connected variables and the gaps in the literature.

Advances in the care for premature neonates are undeniable, as they have considerably reduced their morbidity and mortality. However, despite the implementation of interventions aimed at the family in the NICU setting, it is essential that this assistance be expanded and that there is a multidisciplinary follow-up not only in the neonatal period, but also during the whole childhood. The empirical evidence found supports the notion that these actions will minimize parental suffering.