title: The normal variabilities of the menstrual cycle.
abstract: OBJECTIVE
  To address conflicts in the normal variabilities of the menstrual cycle using the newest generation test methods and to establish normal ranges for use in clinical practice.
  
  
  METHODS
  Daily urine samples were collected from 167 women eager to achieve pregnancy. Samples were tested prospectively for LH and total hCG. A total of 458 nongestational and 111 gestational menstrual cycles were evaluated.
  
  
  METHODS
  Division of Women's Health Research, University of New Mexico.
  
  
  METHODS
  One hundred sixty-seven women desiring pregnancy.
  
  
  METHODS
  None.
  
  
  METHODS
  Levels of hCG and LH.
  
  
  RESULTS
  Menstrual cycles were 27.7 +/- 2.4 days in length. The LH peak indicated the onset of the presumed ovulatory window, which occurs at 14.7 +/- 2.4 days. Implantation (first day of sensitive detection of hCG) occurred in gestational menstrual cycles at 24.6 +/- 3.1 days, or 4.3 +/- 2.2 days before missing the expected onset of menses.
  
  
  CONCLUSIONS
  Our data confirm epidemiological studies on menstrual cycle length and variability and hormonal studies on timing of the ovulatory window and its variability. They dispute, however, the published data on the timing and variance of implantation. As shown, implantation is limited to a 10-day interval culminating in the day of the expected onset of menses. Reference range data provide guidelines for differentiating normal and problem menstrual cycles.
authors.affiliation: Department of Obstetrics and Gynecology, University of New Mexico, Albuquerque, NM 87131, USA. Larry@hcglab.com
authors.forename: Laurence A
authors.initials: LA
authors.lastname: Cole
authors.forename: Donald G
authors.initials: DG
authors.lastname: Ladner
authors.forename: Francis W
authors.initials: FW
authors.lastname: Byrn
mesh_terms: D000293:Adolescent; D000328:Adult; D006063:Chorionic Gonadotropin / Q000652:urine*; D010064:Embryo Implantation; D005260:Female; D006801:Humans; D007986:Luteinizing Hormone / Q000652:urine*; D008597:Menstrual Cycle / Q000652:urine*; D010060:Ovulation; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D013997:Time Factors; D055815:Young Adult
chemical_list: D006063:Chorionic Gonadotropin; D007986:Luteinizing Hormone