Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Lactational amenorrhea
Amenorrhea itself is not necessarily an indicator of infecundity, as the return of ovarian cycling is a gradual process and full fecundity may occur before or after first postpartum menses. Additionally, spotting or the appearance of first postpartum menses can be a result of either lochia or estrogen withdrawal and not actual ovulation. lactational amenorrhea has evolved as a mechanisms for preserving the health of the mother. This period of infecundity allows the mother to focus her energy on breastfeeding as well as allow time for her body to heal between births. The frequency and durations of the feedings determine how long the mother will continue to be infecund during breastfeeding. However there is variation across different cultures. The Turkana, Gainj, and Quechua societies all breastfeed on demand until their child is around 2 years old. The timing of returned ovulation for these women is however varied. Because of this interbirth intervals vary across these three societies.