title: Variability of day 3 follicle-stimulating hormone levels in eumenorrheic women.
abstract: OBJECTIVE
  To assess the intercycle variability of early follicular follicle-stimulating hormone (FSH) and estradiol (E2) levels in eumenorrheic women according to age.
  
  
  METHODS
  Forty-eight female volunteers with regular menstrual cycles were studied. Serum samples were obtained on cycle day 3 in multiple cycles over a one-year period. Serum was also obtained on consecutive cycle days 2, 3 or 4 in a single cycle in 20 participants. All samples were assayed for FSH and E2 by radioimmunoassay.
  
  
  RESULTS
  In women under 40 years of age, all initial day 3 FSH levels were < 20 mIU/mL, and 15% of subjects had a subsequently elevated day 3 FSH level (> or = 20 mIU/mL) within the year. In eight women 40-44 years of age, 75% had an initial day 3 FSH level < 20 mIU/mL, but half of them subsequently had an elevated level, > 20 mIU/mL, within the year. Between cycle days 2, 3 and 4, FSH (coefficient of variation [CV] = 14.8%, 95% confidence interval (CI) = 11.4-18.3%) varied less than E2 (CV = 31.1%, 95% CI = 21.5-40.6%).
  
  
  CONCLUSIONS
  A single day 3 FSH level < 20 mIU/mL is highly predictive of all subsequent values within a year and occurred only in women under 40. An FSH level drawn on cycle day 2 or 4 will probably be within 18% of the day 3 value, but the E2 level may vary by up to 40%.
authors.affiliation: Department of Obstetrics and Gynecology, New York Hospital-Cornell Medical Center, New York.
authors.forename: J R
authors.initials: JR
authors.lastname: Brown
authors.forename: H C
authors.initials: HC
authors.lastname: Liu
authors.forename: K F
authors.initials: KF
authors.lastname: Sewitch
authors.forename: Z
authors.initials: Z
authors.lastname: Rosenwaks
authors.forename: A S
authors.initials: AS
authors.lastname: Berkeley
mesh_terms: D000328:Adult; D000367:Age Factors; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D006801:Humans; D008597:Menstrual Cycle / Q000097:blood*; D008875:Middle Aged; D011446:Prospective Studies; D011863:Radioimmunoassay; D013997:Time Factors
chemical_list: D004958:Estradiol; D005640:Follicle Stimulating Hormone