Fertil Steril. 1981 Nov;36(5):591-8. doi: 10.1016/s0015-0282(16)45856-5.
A five-country prospective study was undertaken to determine the effectiveness of the ovulation method of natural family planning. After successful completion of a teaching phase of three cycles, 725 subjects entered a 13-cycle effectiveness phase and contributed 7514 cycles of observation. The overall cumulative net probability of discontinuation for the effectiveness study after 13 cycles was 35.6%, 19.6% due to pregnancy. Pregnancy rates per 100 woman-years calculated using the modified Pearl index were as follows: conscious departure from the rules of the method, 15.4; inaccurate application of instructions, 3.5; method failure, 2.8; inadequate teaching, 0.4; and uncertain, 0.5.
开展了一项五国前瞻性研究，以确定自然计划生育排卵法的有效性。在成功完成三个周期的教学阶段后，725名受试者进入了为期13个周期的有效性阶段，并提供了7514个观察周期。有效性研究在13个周期后的总体累积净停用概率为35.6%，其中19.6%是由于怀孕。使用改良的佩尔指数计算的每100妇女年妊娠率如下：故意违反方法规则，15.4；说明应用不准确，3.5；方法失败，2.8；教学不足，0.4；以及不确定，0.5。
