Stanford Joseph B, Duane Marguerite, Simmons Rebecca
Office of Cooperative Reproductive Health, Division of Public Health, University of Utah School of Medicine, Salt Lake City, UT, US.
Department of Family Medicine, Georgetown University, Washington DC, US.
Linacre Q. 2024 Aug;91(3):315-328. doi: 10.1177/00243639231212440. Epub 2023 Nov 28.
Fertility awareness-based methods (FABMs), also known as natural family planning (NFP), enable couples to identify the days of the menstrual cycle when intercourse may result in pregnancy ("fertile days"), and to avoid intercourse on fertile days if they wish to avoid pregnancy. Thus, these methods are fully dependent on user behavior for effectiveness to avoid pregnancy. For couples and clinicians considering the use of an FABM, one important metric to consider is the highest expected effectiveness (lowest possible pregnancy rate) during the correct use of the method to avoid pregnancy. To assess this, most studies of FABMs have reported a method-related pregnancy rate (a cumulative proportion), which is calculated based on all cycles (or months) in the study. In contrast, the correct use to avoid pregnancy rate (also a cumulative proportion) has the denominator of cycles with the correct use of the FABM to avoid pregnancy. The relationship between these measures has not been evaluated quantitatively. We conducted a series of simulations demonstrating that the method-related pregnancy rate is artificially decreased in direct proportion to the proportion of cycles with intermediate use (any use other than correct use to avoid or targeted use to conceive), which also increases the total pregnancy rate. Thus, as the total pregnancy rate rises (related to intermediate use), the method-related pregnancy rate falls artificially while the correct use pregnancy rate remains constant. For practical application, we propose the core elements needed to assess correct use cycles in FABM studies.
Fertility awareness-based methods (FABMs) can be used by couples to avoid pregnancy, by avoiding intercourse on fertile days. Users want to know what the highest effectiveness (lowest pregnancy rate) would be if they use an FABM correctly and consistently to avoid pregnancy. In this simulation study, we compare two different measures: (1) the method-related pregnancy rate; and (2) the correct use pregnancy rate. We show that the method-related pregnancy rate is biased too low if some users in the study are not using the method consistently to avoid pregnancy, while the correct use pregnancy rate obtains an accurate estimate.
In FABM studies, the method-related pregnancy rate is biased too low, but the correct use pregnancy rate is unbiased.
基于生育力意识的方法（FABMs），也称为自然计划生育（NFP），能使夫妻识别月经周期中性交可能导致怀孕的日子（“易孕期”），并在希望避免怀孕时在易孕期避免性交。因此，这些方法的有效性完全依赖于使用者的行为来避免怀孕。对于考虑使用FABM的夫妻和临床医生而言，一个需要考虑的重要指标是在正确使用该方法以避免怀孕期间的最高预期有效性（最低可能怀孕率）。为评估这一点，大多数FABM研究报告了方法相关的怀孕率（一个累积比例），它是根据研究中的所有周期（或月份）计算得出的。相比之下，正确使用以避免怀孕率（也是一个累积比例）的分母是正确使用FABM以避免怀孕的周期。这些指标之间的关系尚未进行定量评估。我们进行了一系列模拟，结果表明方法相关的怀孕率会随着中间使用（除正确使用以避免怀孕或有针对性地使用以受孕之外的任何使用情况）周期的比例成比例地人为降低，这也会使总怀孕率增加。因此，随着总怀孕率上升（与中间使用相关），方法相关的怀孕率会人为下降，而正确使用怀孕率保持不变。对于实际应用，我们提出了评估FABM研究中正确使用周期所需的核心要素。
基于生育力意识的方法（FABMs）可被夫妻用于通过在易孕期避免性交来避免怀孕。使用者想知道如果他们正确且持续地使用FABM来避免怀孕，最高有效性（最低怀孕率）会是多少。在这项模拟研究中，我们比较了两种不同的指标：（1）方法相关的怀孕率；以及（2）正确使用怀孕率。我们表明，如果研究中的一些使用者没有持续使用该方法来避免怀孕，那么方法相关的怀孕率会被低估，而正确使用怀孕率能获得准确的估计。
在FABM研究中，方法相关的怀孕率被低估，但正确使用怀孕率无偏差。
