Oral contraceptive use and the incidence of cervical intraepithelial neoplasia.

OBJECTIVE: Our objective was to examine the relationship between oral contraceptive use and the incidence of cervical intraepithelial neoplasia. STUDY DESIGN: In a prospective follow-up study of 6622 women participating in the Second Troms? Study conducted in 1979 and 1980 in Troms?, Norway, women aged 20 to 49 years answered a questionnaire regarding their smoking history, dietary habits, alcohol consumption, and oral contraceptive use. They were then followed for 10 years with data from the Pathology Registry of the University Hospital. RESULTS: The age-adjusted incidence rate of cervical intraepithelial neoplasia was 897 per 100,000 person years among noncurrent and 1295 per 100,000 person years among current oral contraceptive users as of 1979. After adjusting for age, marital status, smoking, and frequency of alcohol intoxication the relative rate for current users was 1.5 (95% confidence interval 1.1 to 2.1), and the relative rate for past users was 1.4 (95% confidence interval 1.0 to 1.8), as compared with those who had never used oral contraceptives before 1979. CONCLUSION: These findings support the hypothesis that the occurrence of cervical intraepithelial neoplasia is increased by oral contraceptive use.