title: Levonorgestrel administration in emergency contraception: bleeding pattern and pituitary-ovarian function.
abstract: BACKGROUND
  This study was conducted to evaluate the effects of levonorgestrel administration for emergency contraception (EC) on bleeding pattern and pituitary-ovarian function.
  
  
  METHODS
  In 69 women with a reported stable menstrual cycle length of 24-34 days, we investigated bleeding patterns following EC administration in the follicular (n=26), periovulatory (n=14) and luteal (n=29) phase. In a subgroup of 8 women, hormonal evaluation and ultrasonography were performed.
  
  
  RESULTS
  EC taken in the follicular, but not in the periovulatory or luteal phase, significantly shortened cycle length by 10.9+/-1 days. The subsequent cycle was not affected. EC taken in the late preovulatory phase, prior to the gonadotrophin surge, suppressed ovulation (n=7), while ovulation was not blocked when EC was given during an ongoing luteinizing hormone (LH) pulse (n=1).
  
  
  CONCLUSIONS
  Our data indicate that EC given before the onset of the luteinizing hormone (LH) surge inhibits ovulation and hastens the end of the current menstrual cycle. Subsequently, the length of the following menstrual cycle returned as prior to treatment. By contrast, levonorgestrel administered after the expected ovulation has no effect on menstrual cycle length.
authors.affiliation: Department of Obstetrics, Gynecology and Pediatrics Sciences, Obstetrics and Gynecology Unit, Policlinico of Modena, via del Pozzo 71, Modena, Italy. alessandra.tirelli@unimore.it
authors.forename: Alessandra
authors.initials: A
authors.lastname: Tirelli
authors.forename: Angelo
authors.initials: A
authors.lastname: Cagnacci
authors.forename: Annibale
authors.initials: A
authors.lastname: Volpe
mesh_terms: D000293:Adolescent; D000328:Adult; D044363:Contraception, Postcoital; D003283:Contraceptives, Postcoital, Synthetic / Q000008:administration & dosage*; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D005498:Follicular Phase / Q000187:drug effects; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage*; D008183:Luteal Phase / Q000187:drug effects; D007986:Luteinizing Hormone / Q000097:blood; D008597:Menstrual Cycle / Q000097:blood / Q000187:drug effects*; D010053:Ovary / Q000187:drug effects* / Q000378:metabolism; D010060:Ovulation / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D011374:Progesterone / Q000097:blood
chemical_list: D003283:Contraceptives, Postcoital, Synthetic; D011374:Progesterone; D004958:Estradiol; D016912:Levonorgestrel; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone