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
Return of menstruation following childbirth varies widely among individuals. This return does not necessarily mean a woman has begun to ovulate again. The first postpartum ovulatory cycle might occur before the first menses following childbirth or during subsequent cycles. A strong relationship has been observed between the amount of suckling and the contraceptive effect, such that the combination of feeding on demand rather than on a schedule and feeding only breast milk rather than supplementing the diet with other foods will greatly extend the period of effective contraception. In fact, it was found that among the Hutterites, more frequent bouts of nursing, in addition to maintenance of feeding in the night hours, led to longer lactational amenorrhea. An additional study that references this phenomenon cross-culturally was completed in the United Arab Emirates (UAE) and has similar findings. Mothers who breastfed exclusively longer showed a longer span of lactational amenorrhea, ranging from an average of 5.3 months in mothers who breastfed exclusively for only two months to an average of 9.6 months in mothers who did so for six months. Another factor shown to affect the length of amenorrhea was the mother's age. The older a woman was, the longer period of lactational amenorrhea she demonstrated. The same increase in length was found in multiparous women as opposed to primiparous. With regards to the use of breastfeeding as a form of contraception, most women who choose not to breastfeed will resume regular menstrual cycling within 1.5 to 2 months following parturition. Furthermore, the closer a woman's behavior is to the Seven Standards of ecological breastfeeding, the later (on average) her cycles will return. Overall, there are many factors including frequency of nursing, mother's age, parity, and introduction of supplemental foods into the infant's diet among others which can influence return of fecundity following pregnancy and childbirth and thus the contraceptive benefits of lactational amenorrhea are not always reliable but are evident and variable among women. Couples who desire spacing of 18 to 30 months between children can often achieve this through breastfeeding alone, though this is not a foolproof method as return of menses is unpredictable and conception can occur in the weeks preceding the first menses.