Indigenous approaches to perinatal mental health: a systematic review with critical interpretive synthesis

Indigenous mothers and birthing parents experience significant inequities during the perinatal period, with mental health distress causing adverse outcomes for mothers/birthing parents and their infants. Limited literature is available to inform our understanding of solutions to these issues, with research primarily focusing on inequities. Our aim was to conduct a systematic review of Indigenous approaches to treatment of perinatal mental health illness. Following the PRISMA guidelines for systematic literature reviews, an electronic search of CINAHL, Medline, PubMed, Embase, APA PsycInfo, OVID Nursing, Scopus, Web of Science, and Google Scholar databases was conducted in January and February 2022 and repeated in June 2022. Twenty-seven studies were included in the final review. A critical interpretive synthesis informed our approach to the systematic review. The work of (Yamane and Helm J Prev 43:167–190, 2022) was drawn upon to differentiate studies and place within a cultural continuum framework. Across the 27 studies, the majority of participants were healthcare workers and other staff. Mothers, birthing parents, and their families were represented in small numbers. Outcomes of interest included a reduction in symptoms, a reduction in high-risk behaviours, and parental engagement/attachment of mothers/birthing parents with their babies. Interventions infrequently reported significant reductions in mental health symptoms, and many included studies focused on qualitative assessments of intervention acceptability or utility. Many studies focused on describing approaches to perinatal mental health distress or considered the perspectives and priorities of families and healthcare workers. More research and evaluation of Indigenous interventions for perinatal mental health illness is required. Future research should be designed to privilege the voices, perspectives, and experiences of Indigenous mothers, birthing parents, and their families. Researchers should ensure that any future studies should arise from the priorities of the Indigenous population being studied and be Indigenous-led and designed. Supplementary Information The online version contains supplementary material available at 10.1007/s00737-023-01310-7.


Introduction
Perinatal mental illness refers to a broad range of psychiatric disorders including mild depression and anxiety, stressrelated disorders, postpartum psychosis, post-traumatic stress disorder, eating disorders, obsessive-compulsive disorders, and anxiety disorders. Disorders present prior to pregnancy, along with those that emerge during pregnancy or the postpartum period, are all considered to be perinatal mental illnesses (O'Hara et al. 2014;Black et al. 2019).
Perinatal mental health research has explored the impact of socio-environmental, psychological, and biological factors on disease and wellbeing across the life span. It is known that high levels of stress and associated mental distress can affect both immediate and long-term outcomes for parent and infant (O'Hara et al. 2014). In many countries, suicide is the leading cause of maternal death (Chin et al. 2022). Parents who are depressed often engage in high-risk behaviours and are less likely to seek or receive adequate healthcare during pregnancy and the postpartum period. Consequences include an increased risk for substance abuse, smoking, exposure to sexually transmitted and other diseases, family violence, poor nutrition, and reduced or absent support systems (O'Hara et al. 2014). These can result in obstetric complications, premature birth, and birth interventions leaving the infant at risk of lower Apgar scores, low birth weight and poor weight gain, poor breastfeeding outcomes, and increased rates of admission to neonatal intensive care units. In the long-term, affected infants are more likely to develop ongoing behavioural, psychological, developmental, and physical challenges (Bowen et al. 2014).
The internationally accepted timeframe for the perinatal period covers pregnancy through to the first year postpartum. However, the time frame of the perinatal period is debatable (O'Hara et al. 2014). Many services and interventions targeting parents and infants take a 'life course approach' and view perinatal mental health as fundamentally connected to the long-term wellbeing of infants. This encompasses the First 1000 days of life and the widely accepted understanding that the period from pregnancy to age 3 years is when the foundation for health and wellbeing is established. (Maternal Care Action Group New Zealand (MCAGNZ) 2022; Linnér and Almgren 2020; Darling et al. 2020). Supporting the mental health of parents during this time is therefore critical. As such, the authors were interested in capturing the impact of services within the first 3 years of life.
Indigenous mothers/birthing parents experience disproportionate levels of mental health illness in the perinatal period compared to the general population (Black et al. 2019;Marriott et al. 2019;Owais et al. 2020). International studies and recent systematic reviews have highlighted disparities in both engagement in services and mental health outcomes for Indigenous populations during the perinatal period (Black et al. 2019;Owais et al. 2020;Tricklebank 2014).). To date, research has primarily focused on describing these inequities, with very little research exploring interventions and approaches to treatment of perinatal mental health that are effective and culturally appropriate for Indigenous populations. As Indigenous women/birthing parents experience a higher prevalence of perinatal mental health distress along with a higher birth rate than their non-Indigenous counterparts, (Bowen et al. 2014), there is a need for better understanding of interventions and approaches that target, and work for, this vulnerable population.
Pre-colonisation, Indigenous populations had systems of health and wellbeing attuned to the environment and concepts of collective and individual wellbeing. The process of colonisation imposed Euro-centric beliefs and systems of health, effectively impeding the self-determination of Indigenous people to manage their health and disrupting their systems of wellbeing (Kirmayer et al. 2003). This, combined with the broader experiences of colonisation such as language degradation, land theft, loss of resources and wealth, discrimination, and the consequent decreased access to the social determinants of health, has led to significant health inequities which persist today for these populations (McCalman et al. 2017;McKinley et al. 2021;Graham and Martin 2016).
Consistent with other areas of health, non-Indigenous models and approaches to treatment of perinatal mental health illness privilege non-Indigenous populations and world-views, perpetuating the inequities experienced by Indigenous peoples. International studies reiterate the need for culturally appropriate evaluation and treatment in the perinatal period for at-risk populations (Marriott et al. 2019). In response, some services and interventions have been adapted in an attempt to serve Indigenous groups more effectively. However, the effectiveness of these interventions in terms of perinatal mental health outcomes needs further exploration.
The aim of this systematic literature review is to identify and synthesise the characteristics of Indigenous approaches to perinatal mental health and wellbeing. The following research questions guided our review 'What are the common characteristics of Indigenous approaches to Indigenous perinatal mental health and wellbeing?' and 'Are Indigenous led interventions that privilege Indigenous values, ways of knowing, and practices, effective for Indigenous mothers and birthing people experiencing perinatal mental health distress?'.
This review followed the approach as recommended by the United Nations (UN) to identify rather than define Indigenous peoples. The UN states: 'Indigenous peoples are the holders of unique languages, knowledge systems and beliefs…their ancestral land has a fundamental importance for their collective physical and cultural survival as peoples. Indigenous peoples hold their own diverse concepts of development, based on their traditional values, visions, needs and priorities' (UN, 2023).
In keeping with a commitment to use inclusive language, the term 'birthing parents' has been used alongside mothers and women throughout this paper.

Methods
Following the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines (Page et al. 2021), we conducted a systematic review of the literature to search for studies examining Indigenous approaches to perinatal mental health. The aim of the review was to identify the characteristics of effective and appropriate approaches to Indigenous perinatal mental health and wellbeing. The PRISMA checklist is included in the supplementary information. A protocol for this review was registered on the international prospective register of systematic reviews (PROSPERO) (registration number: CRD42022346190*).

Eligibility criteria
Studies were eligible for inclusion if they met the following criteria: For population (P), studies included any Indigenous birthing parents/mothers experiencing (or at risk of experiencing) perinatal mental health distress. Intervention/phenomenon of interest (I) is any service, intervention, or model that identified a culturally responsive and/or Indigenous approach that has an impact on mental health and wellbeing during the perinatal period, up to 3 years. Studies exploring the perspectives of Indigenous parents and families on approaches to mental health distress and wellbeing in the perinatal period were also included. For outcomes (O), studies were included if they identified outcomes related to perinatal mental health and wellbeing (such as symptom reduction) and/ or parental-child attachment for Indigenous families. Studies that did not include an Indigenous analysis were excluded. Indigenous analysis engages with Indigenous persons as investigators or partners to extend knowledge significant for those communities. Studies related to mental health beyond the defined perinatal period were also excluded. Only peer-reviewed published studies were included. Qualitative and quantitative studies were included. Inclusion and exclusion criteria are described in full in Table 1.

Literature search
The following databases were searched: CINAHL, Medline, PubMed, Embase, APA PsycInfo, OVID Nursing, Scopus, Web of Science, and Google Scholar. Search terms were structured around perinatal mental health, Indigenous populations, and Indigenous interventions/approaches (see Table 2). No restrictions were applied to study settings or publication dates, and only English language peer-reviewed articles were included. The literature search took place in January and February 2022 and repeated to check for new publications in June 2022. The complete search strategy for the review is included in the supplementary data (Online Resource). The database search was complemented by handsearching the reference lists of included articles and related systematic reviews.
Duplicates were identified and removed using Endnote. Title/abstract screening was completed by (first author) and discussed and refined with co-authors. Full text screening was completed initially by (first author) and then independently reviewed by (co-authors). Any disagreements were discussed by all three authors and consensus met.

Data extraction and analysis
Data extraction and analysis was carried out by first author and discussed with co-authors who have expertise in Indigenous health research. Data items from the studies were extracted and hand-coded in Excel format. Publication date, country and region, Indigenous population, sample size, age range of participants and age range of infant (to ensure study remained within defined perinatal period), setting, study aims and design, method of data collection, analysis, and outcomes were collated. The following data was then extracted and collated: type of intervention, characteristics of the intervention, and cultural characteristics identified within each study. Studies were further organised into a framework identified by Yamane and Helm (2022) that situates interventions on a cultural continuum, identifying approaches that are either culturally adapted, culturally grounded, or promote a 'culture as health' approach.

Quality assessment
In view of the inequities experienced by Indigenous populations in relation to perinatal mental health, we were interested in the responsiveness of the research to the Indigenous populations being studied. We utilised the CONSolIDated criTEria (CONSIDER) statement (Huria et al. 2019) to assess whether studies included equitable and ethical health research practices involving Indigenous populations. The quality of these studies in relation to Indigenous priorities and the advancement of Indigenous health was also assessed using the CONSIDER tool (Meechan and Brewer 2021;Wright et al. 2022). Each of the 17 statements from the CONSIDER criteria was rated (yes (score of 1) or no (0 score)) to provide a total score out of a possible 17.

Data synthesis (i) Critical interpretive synthesis
A critical interpretive synthesis (CIS) informed our approach to the systematic review. This approach was used to synthesise both the qualitative and quantitative research, allowing for the generation of themes and identifying the characteristics of Indigenous approaches to treatment of perinatal mental health illness and distress. CIS integrates evidence from across studies to form a conceptual framework that can be applied to clinical practice and inform future research (Dixon-Woods et al. 2006). Synthesis involved categorising approaches or 'characteristics' commonly identified across all studies.

(ii) Cultural continuum
According to the characteristics identified, a cultural continuum framework was used to distinguish whether the included studies were culturally adapted, culturally grounded, or promoted a culture as health model. These three interpretations draw upon the work of Yamane and Helm (2022). Cultural adaptation is defined as a systematic modification of an evidence-based intervention or programme and considers aspects such as language and culture to become more congruent with the cultural context of the recipient of care (Bernal et al. 2009). Adaptations may be 'surface level' such as using or changing imagery, language, or music to reflect the population being targeted. 'Deep level' adaptations integrate cultural, social, environmental, and spiritual elements (Wiltsey Stirman et al. 2019). Culturally grounded interventions and programs are designed and led by Indigenous peoples, utilise Indigenous ways of knowing, and embed Indigenous values and beliefs. Culture as health progresses this concept and privileges Indigenous ways of knowing, doing, and being, over non-Indigenous approaches, and is defined by the inclusion of four paradigms: Indigenous ways of knowing, Indigenous cultural practices, place-based/sacred sites, and Indigenous spirituality (Yamane and Helm 2022). Culturally grounded interventions are more likely to incorporate non-Indigenous approaches than the culture as health approaches.

Study selection
A total of 3272 articles resulted from our search of the databases. After removing duplicates, 2063 results were screened. Seventy-eight results were eligible for full-text screening. Figure 1 outlines the screening process (PRISMA flowchart) and reasons for exclusion. A total of 27 studies were eligible for inclusion.

Study characteristics
The included studies were published between 2006 and 2022. Included studies were conducted across five countries: USA (n = 10), Australia (n = 8), Canada (n = 4), Aotearoa/ NZ (n = 3), and Guatemala (n = 2). Table 2 describes specific characteristics of the 27 studies included in this review.
The interventions evaluated within the included studies either focused on mental health in the perinatal period or included mental health as part of a wider examination of perinatal health. Interventions evaluated were parenting programmes (n = 8); health programmes (n = 6); mental health-focused interventions (n = 5); cultural interventions (n = 2); family support (n = 1); and an engagement tool (n = 1). Cultural interventions address health and wellbeing holistically, focusing on a balance within health incorporating mind-body, spirituality, culture, language, community, and traditions (Bowen et al. 2014). Engagement tools encourage participation and provide an enticing way of supporting communities to engage in an aspect of healthcare. The remaining studies provided qualitative data on the perspectives of Indigenous peoples on approaches to perinatal mental health.

Participants
Across the 27 studies, a total of 122 birthing parents and family members and 284 healthcare workers or other staff members were included. Of the studies that interviewed recipients of care only, the number of interviewed participants ranged from 14 to 19 in total. Of the healthcare workers and other non-family member participants interviewed, 46% were identified as Indigenous, and 27% were non-Indigenous. Ethnicity of the remaining 27% was either unclear or not stated.

Study outcomes
Outcomes of interest included a reduction in symptoms, a reduction in high-risk behaviours, and parental engagement/ attachment of mothers/birthing parents with their babies. The reporting of outcomes varied across all study types, with the majority of studies not reporting on specific outcomes (see Table 3). These studies were descriptive or designed to inform approaches to perinatal mental health distress and illness in Indigenous populations. Culturally adapted studies were most likely to report on outcomes (63%). Of the culturally grounded studies 33% reported on outcomes. No outcomes were reported or measured within the studies identified as being culture as health.

Quality assessment
Using the CONSIDER statement criteria, studies were determined to have a range of scores from 0 to 12 (out of a possible 17). Common areas of omission (resulting in lower scores) for most studies were around governance or partnership agreements, suggesting an absence of Indigenous leadership. For example, only half of the studies included in this review described how the research emerged from the priorities identified by Indigenous stakeholders (full results of quality assessment are found in the supplementary information (Online Resource). The total scores of each study are found in Table 4 Cultural continuum Of the 27 included studies, 16 were identified to be culturally adapted, six culturally grounded, and five studies met all of the criteria to be distinguished as culture as health approaches (see Table 4). Dominant characteristics of culturally adapted approaches included interventions such as counselling, psychoeducation, and problem solving skills (see S1 table in supplementary information, Online Resource). Culturally adapted approaches also advocated for Indigenous workers who were familiar with the native language and customs, promoting a culturally competent workforce. These characteristics were shared across the culturally grounded and culture as health studies. In this review, culturally grounded and culture as health studies were found to incorporate additional characteristics such as Indigenous practices, values, and spirituality. (Table 4 outlines the cultural characteristics of the included studies and places each study on the cultural continuum as defined by Yamane and Helm (2022)).
The identified characteristics were synthesised into six key themes: skills and education, support systems, relationships, Indigenous self-determination, Indigenous customs and practices, and Indigenous identity.

i) Skills and education
Behavioural skills were identified by 74% of studies alongside problem solving skills (78%). Psychoeducation was identified as a key characteristic in 45% of the studies. This theme was dominant in the culturally adapted and culturally grounded studies and did not feature strongly in the culture as health defined studies.

ii) Support systems
Social supports featured frequently across all studies with 85% of studies highlighting this as a key characteristic. Other forms of support systems included family, therapy or counselling, future planning or goal setting, and addressing the social determinants of health.

iii) Relationships
Relationship building and the development of trust were identified as a key characteristic of 96% of the included studies. Relationships encompassed home visiting, trust building, and trauma informed approaches. Relationships were identified as being developed over time. Culturally adapted studies generally had a recommended or pre-set number of contacts with clients.

iv) Indigenous self determination
Indigenous self-determination encapsulated approaches such as Indigenous leadership, Indigenous healthcare workers, interventions being Indigenously led and designed, involvement of elders, and the expression of self-determination of the Indigenous groups involved in the studies. These approaches all featured strongly in the culturally grounded and culture as health studies. Culturally adapted studies primarily featured the use of Indigenous workers and did not generally identify elders, self-determination or Indigenous design, and leadership as characteristics.

v) Indigenous customs and practices
Family, Indigenous practices, and intergenerational knowledge sharing were all characteristics identified under the theme of Indigenous customs and practices. The role of family was identified as an important approach to perinatal mental health in 85% of the studies. Where characteristics under this theme were not identified, this was generally within the culturally adapted studies.      No outcomes measured vi) Indigenous identity Characteristics such as connection to cultural identity, use of Native language, and connection to Indigenous spirituality were all determined to be categorised under the theme of Indigenous identity. Connection to cultural identity and spirituality were common in both culturally grounded and culture as health studies and were less likely to be found in the culturally adapted studies.

Discussion
This is the first systematic review, to our knowledge, that examines Indigenous approaches to treatment of perinatal mental health illness or distress. Previous systematic reviews in this area have focused on outcomes, screening, and disparities for Indigenous populations experiencing perinatal mental health distress (Black et al. 2019;Marriott et al. 2019;Owais et al. 2020). Despite no restrictions placed on dates of publication, only 27 studies were identified that fit the inclusion criteria. The earliest studies were found in 2006. Interest and publication rate in this area appears to be increasing rapidly with almost half of the included studies being published in the last 5 years. Despite Indigenous peoples inhabiting more than 90 countries globally (United Nations Statistical division State of the World's indigenous peoples 2009), the majority of the included studies were conducted in Australia, Aotearoa, Canada, and the USA. Colonisation and Euro-centric health systems are a shared experience of these countries, which may account for the focus on Indigenous perinatal mental healthcare in these countries and the relative availability of studies.

Characteristics of approaches and the cultural continuum
The themes identified within this review are consistent with other literature exploring perinatal mental health. Social support is identified in several studies exploring perinatal mental health distress in general populations and is found to be protective, reducing the impact of stress during pregnancy, and mitigating the impact of stress during the postnatal period (Lavender et al 2016;Inekwe & Lee 2022;Shorey et al 2015;Li et al 2021). Perinatal interventions that strengthen social support are therefore recommended for both preventing and treating mental health distress. Behavioural and coping skills were also identified as key characteristics within the skills and education theme, aligning with other literature in this area (Lavender et al. 2016). The third theme of relationships aligns with both the Indigenous literature (Flaminio et al. 2020) and non-Indigenous literature. In Indigenous populations, relationships included close family and wider kinship groups, along with health practitioners.   In non-Indigenous literature, these relationships were found in the form of continuity of care models of perinatal care, parenting groups, or peer support programs (Alderdice et al. 2013;Barlow et al. 2012;McLeish and Redshaw 2017). The characteristics identified within the culturally grounded and culture as health studies within this review encompassed three interconnected domains: Indigenous selfdetermination, Indigenous identity, and Indigenous customs and practices. These domains are also considered to be cultural determinants of health (Verbunt et al. 2021), and it is therefore unsurprising that these themes were revealed within this review.
Qualities of self-determination were frequently discussed within the qualitative studies of this review. Indigenous selfdetermination is discussed in wider health literature as being key to Indigenous health and wellbeing. Self-determination is the process by which a person has agency and control over their own life and choices. It is fundamental to addressing power imbalances and ensures Indigenous peoples are involved in every layer of the decision-making process (Verbunt et al. 2021). Experiences that diminish, demean, or disempower an individual, particularly in relation to their cultural identity (Gerlach 2012), impact a person's ability to be self-determining and contribute to poor health outcomes. These culturally unsafe interactions are often a feature when health services are controlled by a system that reflects the dominant science-based biomedical model of care and do not consider or acknowledge cultural or social determinants of health and wellbeing (Haynes et al. 2014).
Indigenous self-determination is innately linked with Indigenous leadership, and both are essential for positive health outcomes (Gallagher 2019). Elders are an inherent feature of Indigenous leadership and are identified as a key characteristic in some of the studies in this review. Elders instil values by way of example, view themselves as a bridge between the past and the future transmitting knowledge to future generations, and have a broader view of wellbeing and health to encompass spiritual realms as much as physical (Muru-Lanning et al. 2021;Verbunt et al. 2021).
Elders are also part of the wider family support and kinship ties that were a strong feature in this review, connecting to the theme of relationships. Kinship ties are viewed as an essential element of health as these relationships and connections have the ability to provide emotional and spiritual support, restoring balance during times of stress and illness (Willing et al. 2020). Kinship ties are a fundamental element of Indigenous identity (Killsback 2019;Monchalin et al. 2020). Cultural identity is a theme that has also been highlighted in other literature as important in connection to health and wellbeing (Brown et al. 2021) alongside connection to spirituality, ancestors, and cultural practices (Verbunt et al. 2021). Traditional healing practices have been highlighted as important for Indigenous health (Asamoah 2022) with traditional ceremonies providing a culturally safe avenue for Indigenous peoples to express feelings and engage with each other, promoting social support and collective transformation (Graham and Martin 2016).
Within this review, the majority of the culturally grounded and culture as health studies advocated or utilised a bicultural approach. A bicultural approach acknowledges the cultural identity of Indigenous peoples and integrates both Indigenous and non-Indigenous knowledge and practices (Eketone and Walker 2015). Interventions within the included studies generally incorporated biomedical approaches to mental health such as psychoeducation and counselling, alongside cultural practices or the integration of Indigenous values. Within the qualitative studies, recipients of care recognised the value of both approaches.
Indigenous concepts such as Two-Eyed Seeing and He awa whiria align with this dual approach. Two-Eyed Seeing is a conceptual framework introduced by Mi'kmaw Elder Albert Marshall in the mid-2000s (Broadhead and Howard 2021) that promotes viewing the world with one eye grounded in Indigenous knowledge with the other eye grounded in non-Indigenous knowledge. He awa whiria or 'braided river' is another Indigenous metaphor arising from a Māori worldview that considers the relationship between Māori and non-Māori streams of knowledge and creates space for both to integrate (Cram et al. 2018). Integrating both knowledge utilises the strengths of both and provides a more holistic approach (Wright et al., 2022;Liebenberg et al. 2022;Asamoah 2022). Wider mental health research has argued that interventions for Indigenous people need to be holistic in their approach, encompassing emotional, spiritual, physical, and mental wellbeing as well as being congruent with Indigenous culture and focusing on both the social and cultural determinants of health (Graham and Martin 2016;Dudgeon and Bray 2018;Liebenberg et al. 2022).
Cultural determinants or 'cultural modes' (Kitayatna et al. 2007) include customs, language, and values. Cultural modes are fundamental to health and wellbeing as they are related to self-esteem and cultural identity. They offer protection against stress and anxiety and provide the context for how people navigate social and health needs (Subica and Uchida 2022). This protection may be disrupted when cultural trauma (such as loss of land or language or any trauma affecting cultural identity) is experienced, impacting a person's (or community's) health and wellbeing (Subica and Uchida 2022).
The incorporation of cultural modes is supported within a bicultural model of care and can potentially mitigate the impact of cultural trauma. This approach also addresses the discord between the dominant biomedical system and the beliefs and perspectives of Indigenous peoples, promoting engagement with services (Sylliboy and Hovey 2020), Liebenberg et al. 2022). Re-engagement with Indigenous cultural and healing practices develops resilience and strength (Kopua et al. 2020) and can contribute to supporting better outcomes.
Improved outcomes in the perinatal period prevents the long-term negative health impacts on both parent and child, disrupting intergenerational cycles of negative impact on affected individuals and their families (Wilkinson et al. 2022). There is evidence that untreated perinatal mental health illness represents a heavy economic burden globally. Addressing this global issue would not only benefit the health and wellbeing of mothers/birthing parents and their families, but would also decrease the burden on health and social services, widely benefiting society as a whole. (Luca et al. 2020). In view of the health, social, justice, education, and economic disparities present for Indigenous populations globally, it is imperative that the perinatal wellbeing of Indigenous peoples be prioritised.

Limitations
Limitations of this review are threefold. Firstly, the perinatal mental health of Indigenous people is relatively under researched, with literature primarily focused on disparities rather than efficacy of interventions. In particular, literature around Indigenous populations outside of Australia, New Zealand, the USA, and Canada was scarce. Secondly, both the paucity of literature and the heterogeneity of the studies made synthesis challenging and findings inconclusive. While psychotherapy and counselling were found to be common features of many studies, they were not described in detail, further limiting any attempts at analysis. Outcome measurements were inconsistent across studies, with some measurement tools validated for Indigenous populations, others not. Many studies did not measure or record outcomes.
Whilst culturally grounded and culture as health interventions are advocated for, there is minimal data and evidence for these types of interventions in the perinatal period. Much of the available literature focused on the description of programmes and approaches. Consequently, the perspectives of healthcare workers and the wider community dominated. These studies were included to ensure that the perspectives of parents and their families involved within these studies were not missed. However, the voices of those directly affected by perinatal mental health illness were diluted, compounding the inconsistency of available data. No studies examined the consistency between provider and patient views, and very few studies examined the interplay between provider and Indigenous pregnant/postpartum person on perinatal distress. The inclusion of the perspectives of birthing people affected by perinatal mental illness is of particular importance. This is to ensure that identified outcomes have relevance and meaning to the population involved (Kersting et al. 2022). Insights from recipients of care and their families can support a balanced and comprehensive assessment of outcomes and efficacy of treatment.
Finally, the CONSIDER quality assessment tool has identified that most of the literature is weak in terms of its ability to be inclusive of Indigenous people and cultural appropriateness of the research for these groups. This is consistent with the wider literature. A recent review of Indigenous methodologies used in maternity research revealed that less than 2% of articles described or reported all Indigenous research principles, and 71% of articles did not report on Indigenous people's involvement (Patterson et al. 2022). Much Indigenous literature is unpublished, and this review may have been strengthened had it included grey literature such as reports and evaluations on Indigenous perinatal mental health initiatives.

Conclusion
Approaches for Indigenous mothers, birthing parents, and their families experiencing perinatal mental health illness were identified in this review and highlighted bicultural and holistic approaches. The gaps within the research of Indigenous perinatal mental health have been identified: (1) The voices of Indigenous mothers, birthing parents, and their families are limited within the available literature. (2) Research about Indigenous programmes addressing mental health illness during the perinatal period is sparse. (3) There is a low number of peer-reviewed studies documenting outcomes and characteristics of Indigenous interventions. These gaps demonstrate the need for more research and evaluation of interventions. Of particular note, Aotearoa NZ had three studies within this review, and only one of these was related to an intervention. This paucity in available literature is consistent with other reviews exploring Indigenous interventions (Richer and Roddy 2022;Moses et al. 2022). Finally, important questions are raised around research practices and ensuring that research in this area arises from priorities identified by Indigenous communities, is Indigenous led, and has meaningful impact for the community being researched. Future research should be designed to privilege the voices, perspectives, and experiences of Indigenous mothers, birthing parents, and their families. Developing culturally appropriate services and programmes is crucial in order to address the immediate and long-term inequities faced by Indigenous families and communities. Research is required to inform effective and accessible interventions for Indigenous peoples experiencing mental health distress in the perinatal period.

Declarations
Ethical statement This manuscript is a systematic review. Only published articles were accessed and used as evidence. Ethical approval was not required.
Informed consent This manuscript is a systematic review. No individual participants involved; therefore, informed consent process is not applicable.

Competing interests The authors declare no competing interests.
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