THE ANTIFERTILITY EFFECTIVENESS OF LOW DOSES OF ETHINYL ŒSTRADIOL

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Abstract
Ethinyl œstradiol, 0.05 mg, was given daily for 25 days from the first day of menstruation to 193 women over 439 cycles. Each treated cycle followed an ovulatory cycle, so that it corresponded to the first cycle of administration of an oral contraceptive which depended on this dose and type of oestrogen for its antifertility effect. Ovulation was suppressed in 175 women (90% of those studied). Analysis of those who ovulated during one or more of the treated cycles revealed that all but five subjects who ovulated were over the age of 25 years, and had natural menstrual cycles which were usually shorter than 27 days. When ovulation occurred during a treated cycle, ovulation was delayed for an average of seven days. Half the population studied did not ovulate in the first cycle treated with ethinyl œstradiol in a dosage of 0.03 mg per day for 25 days from the first day of menstruation. The greater the length of the natural menstrual cycle, the more reliable are low doses of ethinyl œstradiol in suppressing ovulation. Ethinyl œstradiol is more reliable in suppressing ovuation in women aged under 25 years than in older women.