Effect of single administration of levonorgestrel on the menstrual cycle.
BACKGROUND
Levonorgestrel (LNG) 1.5 mg administered within 72 h of unprotected coitus is an established method of emergency contraception. Currently, there is some, although incomplete, knowledge about the mechanism of action.


METHODS
We administered 1.5 mg LNG peri-ovulatory to determine the effects on serum gonadotrophins, estradiol and progesterone levels. Fourteen women were studied in a pretreatment and treatment cycle; eight women (Group A) took LNG 3 days before the expected day of ovulation, while 6 (Group B) took LNG a day before the expected day of ovulation.


RESULTS
The women in Group A had a significant delay in their LH peak and onset of the next menses compared with their pretreatment cycles (26.4 vs. 39.1 days, p<.05). Those in Group B had no significant changes in the endocrine parameters but there was a significant shortening of the mean cycle length in comparison with their pretreatment cycles (25.1 vs. 20.2 days).


CONCLUSIONS
Levonorgestrel 1.5 mg acts as an emergency contraception by delaying the LH surge and interfering with ovulation. It may also disrupt corpus luteum formation causing premature luteinization of unruptured follicles.
Okewole
Idris A
IA
Department of Obstetrics and Gynaecology, Olabisi Onabanjo University Teaching Hospital, Sagamu, P.M.B. 2001, Sagamu, Ogun State, Nigeria. idrisokewole@yahoo.com
Arowojolu
Ayodele O
AO
Odusoga
Okanlawon L
OL
Oloyede
Olufemi A
OA
Adeleye
Olufemi A
OA
Salu
Jide
J
Dada
Olukayode A
OA
D000328:Adult; D044363:Contraception, Postcoital; D003271:Contraceptive Agents, Female / Q000008:administration & dosage / Q000494:pharmacology*; D003338:Corpus Luteum / Q000187:drug effects*; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000187:drug effects*; D008597:Menstrual Cycle / Q000187:drug effects*; D010902:Pituitary Gland / Q000187:drug effects
D003271:Contraceptive Agents, Female; D016912:Levonorgestrel; D007986:Luteinizing Hormone