Background: Becoming a parent has been highlighted as a period associated with increased risks for loneliness, with around one-third of parents reporting feeling lonely often or always. However, as most understanding of loneliness is based on elderly or student cohorts, further insights into the costs of parental loneliness is needed. Method: We conducted a literature review of impacts of loneliness in pregnancy and parenthood and present a synthesis of the health, social, societal, and economic costs. We draw on evidence about impacts and costs of loneliness in other cohorts to help provide a wider context to understand the impacts and costs and how parental loneliness differs from other populations. Results: Similar to literature with elderly cohorts, parental loneliness has impacts on health and wellbeing, such as depression in new parents and increased general practitioner (GP) visits in pregnancy. But also has intergenerational impacts via its association with poor mental health and social competence and increased respiratory tract infections in the child. Physical health impacts widely associated with loneliness in other cohorts have yet to be examined in parents. Loneliness in parents is likely to result in social withdrawal further isolating parents and wider societal and economic costs relating to absence from employment and informal caring roles. Conclusion: Parental loneliness has the potential for negative and pervasive impacts. As parental loneliness has wide ranging and intergenerational impacts it is important that a multi-sectoral perspective is used when examining its costs.