Effectiveness study of the sympto-thermal method: a Canadian sample.

The results of a 2-year international prospective study on the effectiveness of the Sympto-Thermal method of family planning are reported. The overall failure rate was 7.5 pregnancies/100 woman-years (Pearl formula). The cumulative failure rate was 10.4% at the end of the 1st year and 14.2% at the end of the 2nd year. In the Canadian sample (168 couples) the cumulative failure rate was 8.2% at the end of the 1st year and 11.8% at the end of the 2nd year. The most significant variable affecting the reliability of the method was the purpose for which the method was adopted. Those couples who practiced the method for the purpose of delaying the next conception had a pregnancy rate of 14.9/100 woman-years with a cumulative rate of 14.1% for the 1st year and 27.7% for the 2nd year. In contrast those who adopted the method to prevent any future conceptions had a cumulative pregnancy rate of 1% at the end of the 1st year and 2.1% at the end of the 2nd year. This difference underscores the influence of motivation on the use-effectiveness of the Sympto-Thermal method of family planning.