The HHf2 study examined health behaviour during pregnancy before and after a comprehensive health campaign which ran from 1984 to 1987 and targeted pregnant women in Odense, Denmark. Furthermore, lifestyle habits were compared before and during the campaign with similar habits in Aalborg, Denmark. All 13,815 pregnant women (equal numbers from each city) were enrolled in the study, and 11,980 gave information on eating, drinking, and smoking habits during pregnancy. A follow-up study was conducted between 2013 and 2018, in which questionnaire follow-ups of the children and comprehensive register follow-ups of both mothers and children allowed for investigations into how exposures in early life affect health from a lifecourse perspective.