Oral contraceptive type and functional ovarian cysts.

OBJECTIVE

We tested the hypothesis that multiphasic, low-dose monophasic, and high-dose monophasic oral contraceptives share a common protective effect against functional ovarian cysts.

STUDY

DESIGN

We conducted a cohort study using the automatic files of Maine Medicaid to assemble a population of 7462 women between the ages of 15 and 44 who were prescribed an oral contraceptive between Jan. 1, 1987, and Dec. 31, 1988. We included as cases 32 women with a principal diagnosis of a functional ovarian cyst confirmed by medical records as being greater than 20 mm in diameter.

RESULTS

At comparison with the absence of an oral contraceptive prescription, we observed decreasing rates of functional ovarian cysts among women prescribed multiphasic pills (rate ratio 0.91, 95% confidence interval 0.3000 to 2.31), low-dose monophasic pills with less than or equal to 35 micrograms estrogen (rate ratio 0.52, 95% confidence interval 0.17 to 1.33), and high-dose monophasic pills with greater than 35 micrograms estrogen (rate ratio 0.24, 95% confidence interval 0.01 to 1.34).

CONCLUSIONS

The protective effect of oral contraceptives against functional ovarian cysts reported previously for high-dose monophasic pills may be attenuated with newer pills of lower hormonal potency.