Incidence of breakthrough bleeding during oral contraceptive therapy

A phase IV, open-label, multicenter survey of 983 obstetrician-gynecologists was conducted to evaluate the incidence of intermenstrual bleeding in 6,382 women receiving a low-dose monophasic oral contraceptive, ethynodiol diacetate, 1 mg, with ethinyl estradiol, 35 micrograms (EDA 1 mg with EE 35 micrograms) over a six-month period. Most patients (75%) did not experience intermenstrual bleeding during therapy. Follow-up questionnaires were sent to the physicians of the 1,526 women reporting breakthrough bleeding or spotting; 1,027 follow-up questionnaires (67%) were returned. The questionnaires revealed that approximately one-fifth of the patients were placed on EDA 1 mg with EE 35 micrograms to regulate preexisting bleeding; of them, 71% reported an improvement, 13% reported worsening, and 16% reported no change in their cycle regularity. Most breakthrough bleeding or spotting (91%) occurred in the first three months of therapy in women with preexisting irregular bleeding as well as in those using the oral contraceptive solely for birth control. Although a fair proportion of women experienced intermenstrual bleeding, very few (5.1%) discontinued therapy because of it. Thus, the study demonstrated that the incidence of breakthrough bleeding and spotting appears to be within or below the range reported for other monophasic and multiphasic oral contraceptives. Further, in agreement with previously published reports, the data suggest that cycle control will improve after three months of oral contraceptive use.