Effectiveness of the sympto-thermal method of natural family planning: an international study
Rice, F.J.; Lanctôt, C.A.; Garcia-Devesa, C.
International Journal of Fertility 26(3): 222-230
1981
ISSN/ISBN: 0020-725X PMID: 6118343 Document Number: 460309
Motivated and informed participants were recruited for a statistical evaluation of the effectiveness of the symptothermal method. Couples in 5 countries were selected on the following criteria: the wife was between 19 and 44, the wife was of proven fertility by having carried a fetus for at least 28 wk, the couple submitted 1 satisfactory temperature graph before being accepted and the couple must express a willingness to submit temperature graphs for 24 mo. Of the 1022 couples selected, 826 completed the 2 yr; only 35 were lost to follow-up. Cycle length varied from 9-98 days, with an average of 28.43 days. Only 205 women had a variation of 8 days or less. A more complete analysis of the menstrual cycle data will be reported in another paper. The 1022 couples contributed 21.736 cycles and reported 128 unplanned pregnancies, a rate of 7.47 conceptions/100 woman-yr of exposure. Only 16 pregnancies occurred when the couples were following instructions, giving a theoretical effectiveness of .93 pregnancies/100 woman-yr using the Pearl formula. Couples trying to prevent any pregnancies had a failure rate of 4.13%; those only delaying a pregnancy had a failure rate of 14.83%. The symptothermal method used alone had a failure rate of 7.16% while use of contraceptive devices with the symptothermal method had a failure rate of 8.19%. The women in our sample averaged 13 cycles per year. A valid comparative figure for NFP should be expressed in pregnancies per 1300 cycles according to the modified Pearl index rather than per 1200 mg. This gives a pregnancy rate of 7.66% as compared to 7.47% for 1200 mo.