Background: Maternal mental well-being and social circumstances during pregnancy and early childhood impact the child's well-being and development. Supportive and sensitive parenting is one of the strongest predictors of positive emotional, social and behavioral outcomes for the child. Knowledge is needed about how to detect and support vulnerable families already during pregnancy and in the postnatal period. The aim of this study is to assemble and evaluate an interdisciplinary cross-sectoral intervention to promote maternal sensitivity among women with psychological or social vulnerabilities. Methods/design: This randomized controlled trial tests the efficacy of an intervention program in the perinatal period compared to care as usual in enhancing maternal sensitivity in a group of psychologically or socially vulnerable women in the Capital Region of Denmark. The intervention consists of four components: 1) detecting symptoms of mental illness in vulnerable pregnant women and initiating treatment if indicated, 2) strengthening parenting skills using the Circle of Security Parenting program, 3) supporting breastfeeding, and 4) sharing knowledge and organizing treatment pathways for families across sectors. Seventy-six families will be randomly assigned to the intervention or care-as-usual. Data will be obtained at study inclusion at 3-5 months of pregnancy, eight weeks after childbirth, and nine months after childbirth. The primary outcome is maternal sensitivity. Secondary outcomes include infant's socio-emotional development, parents' mentalization, parental stress, depressive symptoms, and parental wellbeing. Qualitative data will provide insight into the implementation process.