title: Retrospective vs. prospective coital frequency and menstrual cycle length in a contraceptive effectiveness trial.
abstract: OBJECTIVE
  To determine how well information at enrollment would predict coital frequency and menstrual segment length during a prospective contraceptive effectiveness trial.
  
  
  METHODS
  We compared retrospective reports of monthly coital frequency and menstrual segment (cycle) length with prospective information for women participating in a contraceptive trial of the Reality((R)) female condom.
  
  
  RESULTS
  Participants reported slightly higher mean monthly coital frequency and slightly longer menstrual segments prior to the study than during the study (12.6 acts vs. 12.0 acts per month and 30.8 days vs. 28.4 days). We examined the actual distribution of differences between the retrospective and prospective measures and found considerable variability. Among the 195 participants studied, parous women were less likely to predict accurately menstrual segment length (OR 0.4; 95% CI 0.3--0.9), while older women were more likely to predict accurately coital frequency (OR 1.9; 95% CI 0.9--3.3).
  
  
  CONCLUSIONS
  Coital frequency and menstrual segment length vary considerably over time. Hence, prospective data collection is essential to accurately characterize these variations and to properly interpret results from contraceptive trials and other studies concerned with fecundability and hazards of reproduction.
authors.affiliation: Family Health International, Research Triangle Park, NC 27707, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Steiner
authors.forename: I
authors.initials: I
authors.lastname: Hertz-Picciotto
authors.forename: D
authors.initials: D
authors.lastname: Taylor
authors.forename: V
authors.initials: V
authors.lastname: Schoenbach
authors.forename: A
authors.initials: A
authors.lastname: Wheeless
mesh_terms: D000328:Adult; D003075:Coitus; D019111:Single-Use Internal Condom; D003268:Contraception Behavior; D005260:Female; D006801:Humans; D016015:Logistic Models; D008597:Menstrual Cycle / Q000502:physiology*; D011446:Prospective Studies; D012189:Retrospective Studies; D011795:Surveys and Questionnaires