Rates of substance abuse in women are on the rise [1–4]. Research suggests that women are more vulnerable to the adverse physiological consequences associated with substance abuse . Substance abuse in women is also associated with a unique constellation of risk factors and needs, including increased prevalence of mental health problems, histories of physical or sexual abuse [6, 7], serious medical problems, poor nutrition, relationship problems (including domestic violence), and deficits in social support [8, 9]. These unique risk factors and presenting needs of women have resulted in the development of numerous women-specific comprehensive treatment models that address the full range of needs and include components such as trauma-specific and trauma informed therapy .
In addition to adjusting our lens to sharpen our focus on the unique needs of women, there is also a need to understand women who abuse substances in their role as mothers. The majority of women who abuse substances are of child- bearing age . As such, substance abuse also has implications for child health and parenting. Children born to women who used substances during pregnancy are at greater risk for prematurity, low birth weight, impaired physical growth and development, behavioral problems, learning disabilities, and substance use [2, 11]. Women who continue to abuse substances after childbirth, despite their best intentions are at risk for a wide range of parenting deficits .
Given the specific risks and needs of women with substance abuse issues and their children, researchers, clinicians, and policy makers have recommended that substance use treatment programs address women's physical, social, and mental health needs, as well as children's needs through prenatal services, parenting programs, child care, and other child-centered services [13–15]. This recognition has resulted in the development of numerous integrated (or comprehensive) treatment programs (those that include on-site pregnancy-, parenting-, or child-related services with addiction services) in countries, such as the United States and Canada.
A theoretical rationale for including pregnancy-, parenting-, or child-related services with substance use services is that integrated treatment programs may enhance the impact of substance use treatment because a) integrated programs may reduce barriers to engaging and remaining in treatment (such as lack of adequate child care ), b) integrated interventions may have a synergistic effect (e.g., mental health services for mother may improve mood which may be associated with reduced substance use), and c) parenting and child development services may increase maternal motivation to reduce substance use. Certainly in their development and evaluation of integrated programs, The Centre for Substance Abuse Treatment  has suggested that "treatment that addresses the full range of a woman's needs is associated with increased abstinence and improvement in other measures of recovery, including parenting skills and overall emotional health. Treatment that addresses alcohol and other drug abuse only may well fail and contribute to a higher potential for relapse."
As the number of integrated programs has grown over the past 20 years, empirical evidence about the effectiveness of these programs has accumulated. Although some individual studies examining the effectiveness of integrated treatment programs suggest positive outcomes, the study quality varies, ranging from randomized controlled trials to less rigorous single-group designs. As such, questions remain regarding the robustness of treatment effects relative to non-integrated substance use programs. Many studies have been limited by inadequate statistical power (small sample size), complicating interpretation of results.
A few systematic reviews and a meta-analysis examining outcomes associated with gender specific (women-only) treatment programs have been completed. In a systematic review of 38 studies on substance abuse treatment for women, Ashley et al.  examined six specific components of treatment programs. Programs with prenatal care, child care, and parenting were associated with higher rates of abstinence and reduced substance use. Orwin, Francisco, and Bernichol  conducted a meta-analysis of studies on the effects of substance abuse treatment for women on substance use, maternal well-being, and pregnancy outcomes. Findings suggested that enhancing women-only treatment programs with prenatal care or therapeutic child care added value above and beyond the effects of standard women-only programs. However, neither of these studies specifically focused on integrated programs and they did not include the recent proliferation of studies of integrated programs.
Synthesizing current research on women-specific programs that include child and/or parenting components (i.e., integrated programs) is a pressing task given that 1) increased funding is being directed towards supporting integrated treatment programs, 2) a proliferation of programs have been developed, and 3) an increased number of evaluations have been conducted. Before more resources are spent on these programs and research, existing literature needs to be synthesized to enhance our knowledge and delineate priorities and directions for future research (cf. Cooper & Hedges ). While a synthesis does not provide a conclusive statement about a problem or treatment area, it can provide pivotal information for the field on what can be improved. Precise and reliable research syntheses will assist in ensuring that the next wave of primary research is sent off in the most illuminating direction .
Meta-analysis is well suited to the task of research synthesis and to addressing the limitations in the current literature. First, meta-analysis addresses the problem of low statistical power by allowing the results of small-sample studies to be combined, resulting in increased statistical power. Dennis, Huebner, and McLellan  found that 87% of the studies in Edwards and Steinglass's  meta-analysis of alcoholism interventions did not meet the minimum level of acceptable power, thus placing them at high risk for missing existing treatment effects.
Similarly, in our evaluation of New Choices, an integrated outpatient program, many results were moderate in strength but failed to reach statistical significance . Thus, meta-analysis can increase interpretability of findings and allow more reliable conclusions about treatment effectiveness. Second, the strength of the intervention effect can be determined by meta-analysis through the use of effect size statistics. The strength of observed effects is less influenced by statistical power than tests of significance and is more clinically relevant . Third, the generalizability of findings from a meta-analysis is greater than that of findings from individual studies because meta-analytic findings are based on a diverse set of study samples rather than a single study sample . Fourth, unlike qualitative reviews, meta-analysis allows one to statistically determine if the strength of the treatment effects differs significantly among studies and then to quantitatively examine what factors, such as program, client, and study characteristics, may be responsible for these differences. For example, variations in study quality can be examined statistically for their potential impact on study findings.
Meta-analysis is an appropriate way to combine results even in circumstances where there are few studies and, in fact, the situation is not uncommon. A common misconception is that meta-analysis is applicable only to research areas involving large numbers of studies. However, meta-analysis can be applied effectively to a small number of studies on a focused topic . Some have argued that focused meta-analyses are more relevant to informing policy  and several meta-analyses in the field of substance abuse treatment reflect this approach . According to Cooper and Hedges ,
If the research question is important, it would be interesting to know how much research there is on the problem, even if the answer was none at all... Ultimately the arbiter of whether a synthesis is needed will not be numerical standards, but the fresh insights a synthesis can bring to a field. Indeed, although a meta-analysis cannot be performed without data, many social scientists see value in empty syntheses that point to important gaps in our knowledge.
In this paper, we examine the impact of integrated treatment programs on maternal substance use. We hypothesize that participation in integrated programs is associated with significant improvements in maternal substance use outcomes and that maternal substance use outcomes are significantly better for women participating in integrated programs than women participating in non-integrated programs. We examine the strength of these effects and, if there is variability in effects among studies, we examine client, program, and study characteristics that may moderate the impact of treatment.