The Effectiveness of Natural Family Planning Methods for Birth Spacing: A comprehensive review
Calendar rhythm is in the same range of effectiveness as modern NFP. When calendar rhythm studies are standardized, the projected rhythm pregnancy rates, 15.0 and 18.5 are within the range of modern NFP methods. Unplanned pregnancy rates for the modern NFP methods range between 10 and 20 pregnancies per 100 women per year. Multivariate analysis comparing sympto-thermal and ovulation method unplanned pregnancy rates shows an ST life table rate of 10.2+2.5 and an OM rate of 16.0+3.3. NFP is as effective as barrier methods of birth spacing and can be used very effectively to avoid pregnancy (less than 5 pregnancies per 100 women per year) if the rules are followed.