title: On the frequency of intercourse around ovulation: evidence for biological influences.
abstract: BACKGROUND
  Intercourse in mammals is often coordinated with ovulation, for example through fluctuations in libido or by the acceleration of ovulation with intercourse. Such coordination has not been established in humans. We explored this possibility by examining patterns of sexual intercourse in relation to ovulation.
  
  
  METHODS
  Sixty-eight sexually active North Carolina women with either an intrauterine device or tubal ligation provided data for up to three menstrual cycles. These women collected daily urine specimens and kept daily diaries of intercourse and menstrual bleeding. Major estrogen and progesterone metabolites excreted in urine were used to identify the day of ovulation. The fertile days of the cycle were defined as the 6 consecutive days ending with ovulation. Women contributed a total of 171 ovulatory cycles. Menstrual bleeding days were excluded from analysis.
  
  
  RESULTS
  The frequency of intercourse rose during the follicular phase, peaking at ovulation and declining abruptly thereafter. The 6 consecutive days with most frequent intercourse corresponded with the 6 fertile days of the menstrual cycle. Intercourse was 24% more frequent during the 6 fertile days than during the remaining non-bleeding days (P < 0.001).
  
  
  CONCLUSIONS
  There apparently are biological factors that promote intercourse during a woman's 6 fertile days.
authors.affiliation: National Institute of Environment Health Sciences, Durham, NC, USA. wilcox@niehs.nih.gov
authors.forename: A J
authors.initials: AJ
authors.lastname: Wilcox
authors.forename: Donna Day
authors.initials: DD
authors.lastname: Baird
authors.forename: David B
authors.initials: DB
authors.lastname: Dunson
authors.forename: D Robert
authors.initials: DR
authors.lastname: McConnaughey
authors.forename: James S
authors.initials: JS
authors.lastname: Kesner
authors.forename: Clarice R
authors.initials: CR
authors.lastname: Weinberg
mesh_terms: D000328:Adult; D003075:Coitus / Q000502:physiology*; D005260:Female; D005498:Follicular Phase / Q000502:physiology; D006801:Humans; D010060:Ovulation / Q000502:physiology*; D011446:Prospective Studies