Clinical effectiveness and potential mode of action
Tubal motility, oviduct flow, and ciliary activity are all influenced by estrogens. Tubal insufflation studies suggest that estrogens cause closure of the uterotubal junction in women. Estrogen action may reflect a release from modifications imposed by progesterone and may threaten the functional integrity of the corpus luteum under hypothalamic-hypophyseal control.
Board and Bhatnagar have shown reduced progesterone levels with administration of diethylstilbestrol. Decrease of BBT following use of ethinyl estradiol and diethylstilbestrol support the theory of the luteolytic action of estrogen. After nidation, estrogens have no effect.
Haspels reported on 2000 women treated with ethinyl estradiol (2-5 mg) or diethylstilbestrol (25-50 mg) administered for 5 consecutive days. Method failure was reported with 3 mg/day ethinyl estradiol and 25-30 mg/day diethylstilbestrol. No pregnancies were reported at 5 mg/day ethinyl estradiol and 50 mg/day diethylstilbestrol. Kuchera reported on 1000 cases with no pregnancies following treatment with 50 mg diethylstilbestrol administered within 72 hours of unprotected coitus (for a pregnancy rate of 2.5/1000).
Other estrogens have been used successfully as postcoital contraceptive agents. Use of conjugated equine estrogens administered orally or intravenously within 72 hours of exposure prevented pregnancy. Dienestrol and dienestrol combined with ethynodiol acetate (progestogen) prevented pregnancy. Depot estradiol administered to 12 patients resulted in 2 ectopic pregnancies. Slow release of this estrogen could account for its high failure rate, although results suggest an effect on zygote transport. It is concluded that the best protection against pregnancy will be obtained by administering estrogen as soon as possible after coitus (preferably within 24 hours, no later than 72 and continued for 5 consecutive days).
- The use of estrogens as postcoital contraceptive agents. Clinical effectiveness and potential mode of action, American journal of obstetrics and gynecology, NCBI PubMed PMID: 4577932, 1973.
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