Integrated treatment programs for pregnant and parenting women who use substances operate at the intersection of multiple service systems, including specialized substance use services, the broader health system, child protection, and social services. Our objectives were to describe the composition and structure of community care networks surrounding integrated treatment programs in selected communities in Ontario, Canada. We used a twostage snowball method to collect network data from 5

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... ely selected integrated treatment programs in communities in Ontario. Front-line staff with integrated treatment programs identified their top 5 service partners, who were then contacted and asked to provide the same information (n = 30). We used social network analysis to measure the cohesiveness, reciprocity, and betweenness centrality in the integrated treatment program's ego network. We described network composition in terms of representation of different service types. Across communities, common service partners were child protection, substance use or mental health services, parenting and child support, and other social services. Primary and pre-natal care, opioid agonist therapy, and legal services were rarely named as partners. Networks varied in network cohesiveness, as indicated by connectivity between the service partners and reciprocal ties to the integrated treatment programs. Integrated treatment programs commonly brokered the connections between other service partners. Findings suggest that these integrated treatment programs have achieved a level of success in developing cross-sectoral partnerships, with child protection services, parenting and child support, and social services featuring prominently in the networks. In contrast, there was a lack of close connections with physician-based services, highlighting a potential target for future quality improvement initiatives in this sector. The funders had no role in study design, data collection recommended that substance use services for women attend to their unique needs and contexts, and reduce barriers that make it difficult for women to participate in substance use services (e.g., lack of childcare, fear of loss of child custody, limited services for pregnant women, provider stigma) [3] [4] [5] [6] [7] [8] [9] [10] [11] . Integrated treatment programs have been developed that cater to women who are pregnant or parenting, using case management and service partnerships to overcome the traditional fragmentation of service sectors and offer a comprehensive array of health and social services. Meta-analyses have reported that integrated treatment helps women to reduce their substance use, and is associated with superior maternal mental health, birth and child health outcomes relative to non-integrated treatment [12] [13] [14] [15] . There is no single standard definition or service model for integrated treatment programs for pregnant and parenting women, and no accepted policy or funding standards that dictate a minimum number or type of services or partnerships. In practice, programs that claim to offer integrated treatment contain a heterogeneous mix of services depending on local needs and resources [16] . There is a lack of research on the implementation and delivery of services within integrated treatment programs [17] , and so we know little about the types of service partnerships that programs develop on the ground as they build community care networks for service provision. In this study, we use a network approach to investigate the partnerships between integrated treatment programs and ancillary health and social services, using measures of network composition and structure to contribute to better understandings of the heterogeneity in integrated service delivery across communities. At a conceptual level, integrated treatment programs are guided by a set of core principles and practices, including: care that is holistic, empowering, and tailored to women's needs; strong investment in staff and organizational health; innovative and coordinated partnerships; and supportive policies from multiple service sectors [18] . Specific service complements vary but commonly include specialized substance use services, maternal and child mental health care, pre-natal and primary care, child protection services, parenting programs, child-minding, and supports for social determinants of health (e.g., housing, income supports, transportation assistance) [3, 11, 16, 19] . Programs typically rely on strong collaborative arrangements for service delivery, sometimes with services co-located under a single roof (i.e., a one-stop shop model), with others relying to a greater or lesser extent on formal and informal partnerships with agencies in their communities (i.e., distributed service model). The key idea across service models is that by working together through cross-sectoral and collaborative networks, service providers are better able to meet the complex needs of women and their children [3, 20] . Given the strong role that partnerships play in service delivery, there is value in investigating how the community care networks that underlie integrated treatment programs are structured. Individual services and care providers are embedded within larger health systems, and there is increasing recognition of the utility of using the concepts and methods of social networks research to evaluate this embeddedness and its meaning for service delivery and outcomes [21, 22] . Social network analysis offers a set of methods to map and measure the relationships between actors (e.g., people, organizations, service providers) [23, 24] . Applied to the study of interdisciplinary health coalitions, collaboratives, or care networks, social network analysis can be used to examine the interconnections between service providers or organizations, cross-sectoral partnerships, diversity in network membership, and the existence of silos (i.e., networks or subcomponents of networks comprised of providers of a single discipline or type) [25] [26] [27] . Findings can provide insights into the development and sustainability of health networks, and linked to downstream measures of network efficiency, productiveness, and impacts [28] . Substance use treatment networks for women PLOS ONE | https://doi.org/10.