Results:
We identified 23 eligible studies in this review, involving 9474 pregnant people and 613 postpartum or unspecified people. These studies were conducted in jurisdictions where cannabis was legal, decriminalized and illegal. Most studies were conducted in the United States of America, where states have varying cannabis laws, but cannabis remains federally illegal.
Concerning quality appraisal, the MMAT tool discourages the calculation of an overall score from the ratings of each category, but the quality of included papers was mostly acceptable 42. As recommended, we present the rating for each criterion in Table 2 for the purposes of evaluating the strength of the conclusions of this synthesis. The included studies represent a variety of methodological approaches with roughly equal distribution of qualitative, quantitative, and mixed methods approaches (Table 4). The combined study populations of 10,087 were dominated by Oh et al 2017 52 which had 7627 participants. No partners were included in these studies and none of the postpartum participants were sampled for their experience or perspectives on using cannabis while breastfeeding (Table 4). Accordingly, our review of partner perspectives and the perspectives of lactating people is empty.
Our initial analysis of the entire dataset identified divergent findings across papers, and this divergence was not associated with critical appraisal results. As we engaged in comparative analysis, we identified that much of the divergence was accounted for by the other substances included in the study. When cannabis was studied alone, grouped with alcohol or tobacco, or grouped with other drugs, the focus and hence the findings of each study shifted. Accordingly, we present findings according to comparator groups (Table 5). We present a synthesis of evidence on three main themes that emerged through our inductive analysis: the main decisions faced by participants in these studies; descriptions of risk and benefit; descriptions of how information was sought and used (Table 6).