Contraceptive methods and ovarian cancer risk among Chinese women: A report from the Shanghai Women's Health Study.

Oral contraceptive use is associated with reduced ovarian cancer risk; however, associations with other contraceptive methods, such as intrauterine device (IUD) and tubal ligation, are less clear. Women in China differ from western women in regard to mechanisms and duration of use of contraception. This study was undertaken to evaluate associations between contraceptive methods and ovarian cancer risk using data from the prospective Shanghai Women's Health Study. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated by Cox proportional hazards regression. A total of 174 epithelial ovarian cancer cases were found to occur among 70,259 women who were followed-up for a total of 888,258 person-years. The majority of women had ever used any contraception (77.0%), including IUD (55.6%), oral contraceptive (20.4%), tubal ligation (14.7%) or contraceptive shots (2.6%). Ever use of any contraception was associated with a nonsignificant reduction in ovarian cancer risk (HR: 0.86, 95% CI: 0.60-1.24). Longer duration of IUD use was associated with lower ovarian cancer risk (p-value for trend = 0.04). Compared with never users, women with durations of IUD use longer than the median (20 years) were 38% less likely to develop ovarian cancer (HR: 0.62, 95% CI: 0.40-0.97). Based on the high prevalence and long duration of IUD use among Chinese women, we estimate a preventive fraction of 9.3%, corresponding to approximately 16 ovarian cancer cases. High prevalence of long-term IUD use may, therefore, contribute to the low incidence of ovarian cancer observed in China.