Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden.
Department of Women's and Children's Health, Karolinska Universitetssjukhuset, Stockholm, Sweden.
BMJ Open. 2019 Mar 23;9(3):e026474. doi: 10.1136/bmjopen-2018-026474.
To investigate the association between contraceptive effectiveness of Natural Cycles and users' previous choice of contraceptive, and to evaluate the impact of shifting from other methods to Natural Cycles on the risk of unintended pregnancy.
Natural Cycles mobile application.
16 331 Natural Cycles users in Sweden for the prevention of pregnancy.
Risk of unintended pregnancy.
Real world evidence was collected from Natural Cycles users regarding contraceptive use prior to using Natural Cycles and sexual activity while using Natural Cycles. We calculated the typical use 1-year Pearl Index (PI) and 13-cycle failure rate of Natural Cycles for each cohort. The PI was compared with the population PI of their stated previous methods.
For women who had used condoms before, the PI of Natural Cycles was the lowest at 3.5±0.5. For women who had used the pill before, the PI of Natural Cycles was the highest at 8.1±0.6. The frequency of unprotected sex on fertile days partially explained some of the observed variation in PI between cohorts. 89% of users switched to Natural Cycles from methods with higher or similar reported PIs.
The effectiveness of Natural Cycles is influenced by previous contraceptive choice and this should be considered when evaluating the suitability of the method for the individual. We estimate that Natural Cycles usage can reduce the overall likelihood of having an unintended pregnancy by shifting usage from less effective methods.
研究自然周期避孕效果与使用者先前选择的避孕方法之间的关系，并评估从其他方法转为自然周期对意外怀孕风险的影响。
自然周期移动应用程序。
16331 名在瑞典使用自然周期避孕的女性。
意外怀孕风险。
从自然周期使用者那里收集了关于使用自然周期之前的避孕方法和使用自然周期期间的性行为的真实世界证据。我们计算了每个队列的自然周期典型使用 1 年 Pearl 指数（PI）和 13 个周期失败率。将 PI 与她们之前报告的方法的人群 PI 进行比较。
对于之前使用过避孕套的女性，自然周期的 PI 最低，为 3.5±0.5。对于之前使用过避孕药的女性，自然周期的 PI 最高，为 8.1±0.6。在可受孕日无保护性行为的频率部分解释了队列之间 PI 观察到的差异。89%的使用者从 PI 较高或相似的方法转为使用自然周期。
自然周期的有效性受到先前避孕方法选择的影响，在评估该方法对个体的适用性时应考虑这一点。我们估计，通过将使用方法从效果较差的方法转移，自然周期的使用可以降低意外怀孕的总体可能性。
