The length of the cycle may also vary for a woman during different phases of life, and even from one month to the next depending on a variety of factors, including the woman's physical, emotional, and nutritional health. Menstruation is part of the regular process that prepares a woman's body each month for pregnancy. This cycle involves several phases that are controlled by the interactions of hormones secreted by the hypothalamus, anterior pituitary gland, and ovaries. During pre-ovulation , the cell lining of the uterus begins to develop and thicken. This lining will serve as the anchor for the developing fetus if the woman is impregnated.
Hormones signal an ovum or egg in the ovary to begin developing.
Soon, an ovum is released from the woman's ovary signalling ovulation and begins to move through the Fallopian tube toward the uterus. A woman's luteal phase follows, the period of time which directly follows ovulation. The blood system washes the lining away and it and the blood are discharged through the woman's vadgina. If a woman becomes pregnant, her monthly menstruation ceases for the duration of the pregnancy. Consequently, missing a menstrual period is a likely although not a definitive sign that a woman is pregnant.