title: The effects of peri-ovulatory administration of levonorgestrel on the menstrual cycle.
abstract: Levonorgestrel (LNG) 0.75 mg administered 12 h apart within 72 h of unprotected coitus, is an established method of emergency contraception (EC). The mechanism of action of LNG used in this manner is unknown. We administered LNG 0.75 mg twice immediately before ovulation, to test the hypothesis that LNG acts as an emergency contraceptive by abolishing the pre-ovulatory lutenizing hormone (LH) surge and thereby delaying ovulation. Twelve women took LNG on or before the day of the first significant rise in urinary LH in 12 cycles. In four women, the LH peak and the onset of next menses were significantly delayed (delay of 16.8 days (SD +/- 8.7) from the day of mean LH peak in placebo cycles). One woman did not ovulate at all, despite a normal LH peak and cycle length. In the remaining eight women, LNG did not affect ovulation or the cycle length, but the length of the luteal phase and the total luteal phase LH concentrations were significantly reduced. We suggest that LNG acts as an emergency contraceptive by other mechanisms as well as delaying the LH surge and interfering with ovulation.
authors.affiliation: Contraceptive Development Network, Department of Reproductive and Development Sciences, The University of Edinburgh, Centre of Reproductive Biology, EH3 9ET, Edinburgh, Scotland, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Hapangama
authors.forename: A F
authors.initials: AF
authors.lastname: Glasier
authors.forename: D T
authors.initials: DT
authors.lastname: Baird
mesh_terms: D000328:Adult; D003281:Contraceptives, Postcoital / Q000008:administration & dosage* / Q000494:pharmacology; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage* / Q000494:pharmacology; D008183:Luteal Phase; D007986:Luteinizing Hormone / Q000378:metabolism / Q000652:urine; D008597:Menstrual Cycle / Q000187:drug effects*; D010060:Ovulation / Q000187:drug effects; D011276:Pregnanediol / Q000652:urine; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D003281:Contraceptives, Postcoital; D016912:Levonorgestrel; D007986:Luteinizing Hormone; D011276:Pregnanediol