The report is part of the Maternal Mental Health Alliance's Everyone's Business Campaign which is calling for appropriate care for women experiencing perinatal mental health problems wherever and whenever they need it.
Its key findings reveal that the cost of mental health problems among women in pregnancy are far greater than previously thought; the cost to the public sector of perinatal mental health problems is five times the cost of improving services.
Despite guidance from NICE and other national bodies on the treatment of mental illness during and after pregnancy, the report's authors say current provision is "patchy" with significant variations in coverage around the country.
Lead author Annettte Bauer, from the LSE's Personal Social Services Research Unit, says: "Our findings show that mothers' mental health is vital to the economy and society as a whole, particularly because of the potential negative impact that untreated maternal mental health problems may have on children.
"In order to protect the family's long-term health, intervention needs to start before the child is born, or shortly after because the potential benefits are very high and the costs could be fully recovered in a short time frame."