The symptothermal methods is based on female reproductive anatomy and physiology. After a variable number of days after the onset of menses, an estrogen surge followed by a surge of LH triggers ovulation. The estrogen surge causes the columnar thin stretchy mucus (type E, estrogenic). Type E mucus allows increased sperm penetration and longer sperm survival (3 to 5 days versus hours) and filters out morphologically defective sperm. Several studies have shown that this mucus, detected externally at the vaginal introitus, correlates closely with the time of ovulation. by 3 days following peak mucous production, ovulation occurs in nearly all women. An unfertilized egg can survive 12 to 24 h. Following ovulation, progesterone becomes the dominant hormone. Progesterone is thermogenic, causing the body temperature to rise, and the cervical mucus is changed to an opaque, sticky type (type G, gestagenic). The average length of post ovulatory phase is 13.7 days (range 9 to 17 days, but usually consistent within a given woman).

翻译:
在月经开始后的数天，由于LH 的作用使得会诱发排卵的雌激素也跟着激增。而雌激素的激增导致一种呈柱状、薄且具弹性的黏液产生，此黏液称为E型黏液 (type E, 其中E 就是estrogenic 也是雌激素的意思)，而这个E型黏液，可以增加精子穿透力、延长精子的存活时间（3到5天）并且会将形态有缺陷的精子过滤掉。一些研究显示，这种E型分泌物在外阴道口的量与排卵的时间具有相当密切的关系，大约在E型黏液大量产生的后三天，大部分的妇女会在这个时候排卵。未 受精的卵子可以存活12到24小时。排卵之后，将黄体激素会开始产生。黄体激素会导致体温上升，并使得子宫颈粘液变成不透明且具黏性，此时的黏液称为 G型黏液（G tupe，G为 gestagenic，为妊娠的意思）。排卵期后的平均长度为13.7天就会开始下一周期（范围为9至17天)。

通俗解读:
所谓的"蛋清"应该指的就是E型分泌物，在排卵期前会开始产生，功用是增加精子穿透力、延长精子的存活时间并且会将形态有缺陷的精子过滤掉，看起来都是帮助怀孕的好东西呀~