Parameters of the menstrual cycle and the efficiency of rhythm methods of contraception

Abstract

Further evidence is presented which suggests that in the Ogino and Knaus ‘rhythm’ methods of contraception, the periods of prescribed abstinence are not appropriately centred round the best prediction of ovulation day. It is suggested that with a slight modification, a rhythm method previously described by the author is both more efficient and less demanding than Ogino's system. Theoretical failure rates of various rhythm methods are offered. The variability of pre- and post-ovulatory phase and of total cycle length are considered (a) within single menstrual histories and (b) within a group of women. The correlations between these three variables are discussed.