Calendar rhythm efficacy: a review

Adv Contracept. 1996 Jun;12(2):123-8. doi: 10.1007/BF01849633.


Objective: To estimate the unplanned pregnancy rate of calendar rhythm.

Design: Meta-analysis of eight studies of calendar rhythm published between 1940 and 1989.

Results: There exist few studies of the calendar rhythm method. Analysis of the best of these studies resulted in a conservative estimated Pearl rate of 18.5 +/- 1.8, and a less conservative estimate of 15.0 +/- 4.0, standardized to 12 months' observation; these results are in the range of other natural and barrier methods.

Discussion: We need properly done clinical trials of the calendar rhythm method to scientifically establish its effectiveness.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Female
  • Humans
  • Natural Family Planning Methods*
  • Ovulation Detection / methods
  • Periodicity
  • Pregnancy / physiology
  • Pregnancy / statistics & numerical data*
  • Pregnancy Rate
  • Reproducibility of Results