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
Half the Sky and when seen by patriarchal husbands and affected wives can change household dynamics. Another solution is sponsored by Always, Always provides feminine care products to school girls so that they do not miss school during their menstrual cycle, which often happens because they feel ashamed. The final and probably most empowering solution is an education. Allowing girls to attend school and go beyond elementary school can truly help women advance in developing countries. Carolyn See, a book critic from "The Washington Post", said in her review: "'Half the Sky' is a call to arms, a call for help, a call