BACKGROUND:Several environmental factors have been associated with increased risks for cervical cancer. We examined whether reproductive history, contraceptive use, or sexual behaviour increase the risk for cervical intraepithelial neoplasia grade 3 or worse (CIN3+) among women with persistent human papillomavirus (HPV) infection.METHODS:A population-based cohort of women participated in a personal interview and underwent a gynaecological examination at which cervical specimens were obtained for HPV DNA testing. Follow-up information (~13 years) on cervical lesions was obtained from the Danish Pathology Data Bank. Women who had a high-risk HPV infection comprised the overall study population (n=1353). A subgroup of women with persistent high-risk HPV infection (n=312) was identified. Hazard ratios (HRs) for a diagnosis of CIN3+ and the corresponding 95% confidence intervals (CIs) were calculated.RESULTS:Women with persistent HPV infection who had given birth had a significantly increased risk for CIN3+ (HR=1.78; 95% CI: 1.07-2.94). No association was found with pregnancy, use of intrauterine devices, or sexual behaviour. Based on small numbers, women with persistent HPV infection had a decreased risk for CIN3+ with any use of oral contraceptives (HR=0.54; 95% CI: 0.29-1.00).CONCLUSION:Childbirth increases the risk for subsequent CIN3+ among women with persistent HPV infection.British Journal of Cancer advance online publication, 20 November 2012; doi:10.1038/bjc.2012.513 www.bjcancer.com.