title: Cervical mucus secretions on the day of intercourse: an accurate marker of highly fertile days.
abstract: OBJECTIVE
  To provide estimates of the probabilities of conception according to vulvar mucus observations classified by the woman on the day of intercourse.
  
  
  METHODS
  Prospective cohort study of 193 outwardly healthy Italian women using the Billings Ovulation Method. Outcome measures include 161 conception cycles and 2594 non-conception cycles with daily records of the type of mucus and the occurrences of sexual intercourse.
  
  
  RESULTS
  The probability of conception ranged from 0.003 for days with no noticeable secretions to 0.29 for days with most fertile-type mucus detected by the woman. The probability of most fertile type mucus by day of the menstrual cycle increased from values <20% outside of days 10-17 to a peak of 59% on day 13.
  
  
  CONCLUSIONS
  Regardless of the timing of intercourse in the menstrual cycle, the probability of conception is essentially 0 on days with no secretions. This probability increases dramatically to near 30% on days with most fertile-type mucus, an association that accurately predicts both the timing of the fertile interval and the day-specific conception probabilities across the menstrual cycle.
authors.affiliation: Department of Applied Statistics and Economics, University of Pavia, Pavia, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Scarpa
authors.forename: David B
authors.initials: DB
authors.lastname: Dunson
authors.forename: Bernardo
authors.initials: B
authors.lastname: Colombo
mesh_terms: D002582:Cervix Mucus / Q000378:metabolism*; D003075:Coitus; D005260:Female; D005298:Fertility; D005306:Fertilization; D006801:Humans; D008297:Male; D012252:Natural Family Planning Methods / Q000379:methods; D011247:Pregnancy; D011336:Probability; D011446:Prospective Studies; D013997:Time Factors