title: A randomized trial of three oral contraceptives: comparison of bleeding patterns by contraceptive types and steroid levels.
abstract: OBJECTIVE
  Our purpose was to determine the relationship between bioavailability of contraceptive steroids and bleeding patterns.
  
  
  METHODS
  A randomized clinical trial evaluated 192 women on 50 micrograms of ethinyl estradiol and 1.0 mg of norethindrone (OC1), 35 micrograms ethinyl estradiol and 1.0 mg of norethindrone (OC2), and 35 micrograms ethinyl estradiol and 0.5 mg norethindrone (OC3) over nine cycles.
  
  
  RESULTS
  Intermenstrual bleeding rates were higher for OC3 when compared with OC1 (p = 0.01). The number of intermenstrual bleeding days was highest for OC3 (p = 0.001) and higher for OC2 when compared with OC1 (p < 0.006). The onset of withdrawal bleeding occurred faster in OC3 patients (p < 0.02). Bioavailability of both contraceptive steroids as measured by baseline values and 1-hour slopes did not correlate with bleeding patterns at 3, 6, and 9 months of use.
  
  
  CONCLUSIONS
  These data suggest that differences in biologic responses associated with pill use cannot be explained solely on the basis of these particular hormone measurements.
authors.affiliation: Department of Gynecology and Obstetrics, Henry Ford Hospital, Detroit, MI 48202.
authors.forename: W A
authors.initials: WA
authors.lastname: Saleh
authors.forename: R T
authors.initials: RT
authors.lastname: Burkman
authors.forename: H A
authors.initials: HA
authors.lastname: Zacur
authors.forename: A W
authors.initials: AW
authors.lastname: Kimball
authors.forename: P
authors.initials: P
authors.lastname: Kwiterovich
authors.forename: W K
authors.initials: WK
authors.lastname: Bell
mesh_terms: D001682:Biological Availability; D003276:Contraceptives, Oral / Q000009:adverse effects* / Q000737:chemistry; D004338:Drug Combinations; D004997:Ethinyl Estradiol / Q000008:administration & dosage* / Q000097:blood; D005260:Female; D006801:Humans; D015994:Incidence; D009640:Norethindrone / Q000008:administration & dosage* / Q000097:blood; D009994:Osmolar Concentration; D013997:Time Factors; D014592:Uterine Hemorrhage / Q000139:chemically induced* / Q000453:epidemiology
chemical_list: D003276:Contraceptives, Oral; D004338:Drug Combinations; D004997:Ethinyl Estradiol; D009640:Norethindrone