Menstrual cycle of progesterone, the uterine lining changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing a sharp drop in levels of both progesterone and estrogen. The hormone drop causes the uterus to shed its lining in a process termed menstruation. Menstruation also occurs in closely related primates (apes and monkeys). The average age of menarche is 12–15. They may occasionally start as early as eight, and this onset may still be normal. This first period often occurs later in the developing world
Menstrual cup investigated whether silicone menstrual cups are a viable alternative to tampons and found that approximately 91% of women in the menstrual cup group said they would continue to use the cup and recommend it to others. In a 1991 clinical study involving 51 women, 23 of the participants (45%) found rubber menstrual cups to be an acceptable way of managing menstrual flow. In a randomized controlled feasibility study in rural western Kenya, adolescent primary school girls were provided with menstrual cups or sanitary pads instead of traditional menstrual care items of cloth or tissue. Girls provided with menstrual cups had