Age at first intercourse, number of partners and sexually transmitted infection prevalence among Danish, Norwegian and Swedish women: estimates and trends from nationally representative cross-sectional surveys of more than 100 000 women.

Scandinavian women reported lower age at first intercourse in younger birth cohorts. Moreover, they reported more lifetime sexual partners and a higher prevalence of ever having a sexually transmitted infection in 2012 than in 2005. Our findings may inform the interpretation of trends in outcomes associated with sexual health, and public health policies.