Six hundred ninety-two women were enrolled in a multicenter clinical trial to evaluate a combination of ethinyl estradiol and dl-norgestrel as a postcoital contraceptive. When compared with various formulas predicting the probability of pregnancy in this group, the number of pregnancies observed appears to be reduced by approximately 84%. The combination of 200 micrograms of ethinyl estradiol and 2 mg of dl-norgestrel seems to be effective as a postcoital contraceptive with several advantages over estrogens alone.
PIP: The study purpose was to obtain additional clinical experience with 200 mcg of ethinyl estradiol combined with 2 mg dl-norgestrel as an emergency postcoital contraceptive. Half the dosage was administered immediately upon entry into the study and the remainder 12 hours later. A total of 28 clinics in Canada agreed to participate in the study, but 4 withdrew before entering any cases. Participants were either health services of educational institutions, Planned Parenthood facilities, or hospital based women's clinics. A 24 month enrollment period was chosen, but the largest numbers of subjects were enrolled during a total of 14 months. A total of 692 subjects were enrolled. The total dosage administered was 200 mcg of ethinyl estradiol and 2 mg of dl-norgestrel. 3 of the 24 participating clinics provided 60.1% of the enrolled cases. 120 of the 692 subjects had been pregnant at least once before. 95 of these were regularly cycling, and 25 were irregularly cycling. Subjects were divided into 2 groups, those having regular menstrual cycles and those with irregular cycles. Regular cycles were defined as no more than +or- 5 days variation in cycle length from cycle to cycle. There were 496 regularly cycling women (71.8%) and 194 (28.0%) with irregular cycles. In 2 cases data were lacking regarding cycle regularity. An almost equal number of study subjects were treated within the 1st 24 hours (42.4%) and the subsequent 24 hours (35.6%) following exposure. A further 20.1% were treated between 48 and 72 hours following exposure. A midcycle exposure (MCE) for regularly cycling subjects was calculated from the average cycle length, minus 14 days +or- 3 days. Of 451 who were regularly cycling and for whom data were available, 101 were exposed prior to midcycle, 217 at midcycle, and 133 after midcycle. 11 pregnancies were reported from 6 of the participating clinics. 4 of these women had been pregnant at least once previously. 9 had regular cycles, and 2 had irregular cycles. 4 of the 9 regularly cycling women reported other unprotected coital exposures more than 72 hours prior to treatment during their treatment cycle. 42.4% of the subjects experienced no side effects. Nausea and/or vomiting occurred in 51.7% of the subjects and was absent in 48.3%. Other side effects were infrequent. the combination of 200 mcg ethinyl estradiol and 2 mg of dl-norgestrel appears to be an effective method of postcoital contraception with failure rates comparable to those reported for the estrogens used alone.