The idealized “normal” menstrual cycle typically comprises a coordinated ebb and flow of hormones over a 28-day span with ovulation invariably shown at the midpoint. It's a pretty picture—but rare. Systematic studies have debunked the myth that cycles occur regularly about every 28 days. However, assumptions persist regarding the extent and normalcy of variation in other cycle biomarkers. The processes of judging which phenotypic variants are “normal” is context dependent. In everyday life, normal is that which is most commonly seen. In biomedicine normal is often defined as an arbitrarily bounded portion of the phenotype's distribution about its statistical mean. Standards thus defined in one population are problematic when applied to other populations; population specific standards may also be suspect. Rather, recognizing normal female reproductive biology in diverse human populations requires specific knowledge of proximate mechanisms and functional context. Such efforts should be grounded in an empirical assessment of phenotypic variability. We tested hypotheses regarding cycle biomarker variability in women from a wealthy industrialized population (Germany) and a resource-limited rural agropastoral population (Bolivia). Ovulatory cycles in both samples displayed marked but nonetheless comparable variability in all cycle biomarkers and similar means/medians for cycle and phase lengths. Notably, cycle and phase lengths are poor predictors of mid-luteal progesterone concentrations. These patterns suggest that global and local statistical criteria for “normal” cycles would be difficult to define. A more productive approach involves elucidating the causes of natural variation in ovarian cycling and its consequences for reproductive success and women's health.

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认识正常的生殖生物学：德国和玻利维亚妇女月经周期生物标志物变异性的比较分析

理想化的“正常”月经周期通常包括在 28 天的跨度内协调的激素潮起潮落，排卵总是显示在中点。这是一张漂亮的照片——但很少见。系统研究揭穿了周期大约每 28 天定期发生的神话。然而，关于其他周期生物标志物变异的程度和正常性的假设仍然存在。判断哪些表型变异是“正常”的过程取决于上下文。在日常生活中，正常是最常见的。在生物医学中，正态通常被定义为表型分布中关于其统计平均值的任意有界部分。这样在一个人群中定义的标准在应用于其他人群时是有问题的；特定人群的标准也可能值得怀疑。相当，在不同人群中识别正常的女性生殖生物学需要对相关机制和功能背景的具体了解。这种努力应该以对表型变异性的经验评估为基础。我们测试了关于来自富裕工业化人口（德国）和资源有限的农村农牧人口（玻利维亚）的女性的周期生物标志物变异性的假设。两个样品中的排卵周期在所有周期生物标志物和周期和相位长度的类似平均值/中位数中显示出显着但仍然具有可比性的变异性。值得注意的是，周期和相位长度是黄体中期黄体酮浓度的不良预测指标。这些模式表明，“正常”周期的全局和局部统计标准将难以定义。