Culture and menstruation the ideal of synchronised tidal, lunar, menstrual and seasonal periodicities whose overall harmony (it is believed) confers spiritual power and fertility. To many, such cultural associations appear persuasive in view of the fact that in humans, the menstrual cycle quite closely approximates the moon's 29.5-day synodic cycle, unlike in chimpanzees (~36 days) or bonobos (~40 days). Statistical information from hunter gatherers is lacking, but where large-scale western studies focus on women's peak reproductive years—removing outlier values—the cycle length gravitates around 29.1–29.5 days, while the figure for women in their thirties shortens toward 28 days. In no extant human population has
Menstrual cup find a larger cup uncomfortable. Length also needs to be considered: if a female's cervix sits particularly low, she may want to use a shorter cup. Capacity is important to women who have a heavier flow. The average menstrual cup holds around 20 ml. Some cups are designed to be larger and hold 37–42 ml. However, all cups currently available have a larger capacity than a regular tampon, which is 10–12 ml. A final consideration in selecting a menstrual cup is firmness or flexibility. Some companies offer a range of firmness levels in their cups. A firmer cup pops open