Risk for borderline ovarian tumours after exposure to fertility drugs: results of a population-based cohort study

main results and the role of chance: Analyses within the cohort showed that the overall risk for borderline ovarian tumours was not associated with the use of any fertility drug (RR 1.00; 95% CI 0.67 –1.51) or of gonadotrophins (RR 1.32; 95% CI 0.81 –2.14), clomiphene citrate (RR 0.96; 95% CI 0.64– 1.44), human chorionic gonadotrophins (RR 0.91; 95% CI 0.61 –1.36) or gonadotrophin-releasing hormone analogues (RR 1.10; 95% CI 0.66– 1.81). Furthermore, no associations were observed between the risk for borderline ovarian tumours and these groups of fertility drugs according to the number of cycles of use, length of follow-up or parity. In contrast, use of progesterone increased the risk for borderline ovarian tumours, particularly serous tumours, for which statistically significantly increased risks were observed with any use of progesterone (RR 1.82; 95% CI 1.03– 3.24), among women treated with ≥4 cycles of progesterone (RR 2.63; 95% CI 1.04 –6.64) and for all women followed up for ≥4 years after their first treatment with progesterone. limitations,reasonsforcaution: Although we tried to minimize the effects of the underlying infertility, the severity of infertility might have affected our risk estimates, as women with more severe fertility problems may receive more treatment. The results from the subgroup analyses, e.g. the findings of an elevated risk for borderline ovarian tumours associated with increased time since first use of progesterone and with increased number of treatment cycles, should be interpreted with caution as these analyses are based on a limited number of women with borderline ovarian tumours.