A menstrual period normally occurs once a month in a woman's life from puberty to menopause. The menstrual cycle begins with the maturing of an egg or ovum in the ovaries and ends with the shedding of the lining of the uterus. The levels of estrogen, a hormone produced in the ovaries, rise and fall throughout the menstrual cycle. Increased levels of estrogen cause the uterine lining to thicken. Decreased levels of estrogen cause the shedding of the uterine lining or period. Missing a menstrual period is caused by changes in hormonal levels.
Pregnancy and Breastfeeding
During the first part of the menstrual cycle, estrogen levels increase and allow the lining of the uterus to thicken and prepare for the fertilized egg. The egg is released from the ovary and travels through the fallopian tube to the uterus. A fertilized egg will attach to the wall of the uterus. A pregnant woman will have missed periods because the lining of the uterus is needed to support the development of the fetus.
Estrogen stimulates the production of prolactin, which is a hormone that causes milk production in the breasts. The levels of estrogen remain high and then gradually decrease as the baby is weaned from breastfeeding. Some women may not ovulate or have regular menstrual periods while breastfeeding. This is called lactation amenorrhea.
Lifestyle Stress
Emotional and physical stress can be responsible for a missed menstrual period. Depression and emotional stress, such as bereavement for a loved one or the stress of a new career move, trigger the adrenal glands to produce the hormone called cortisol. High levels of cortisol affect the levels of other hormones, particularly estrogen and progesterone. An increase and a decrease in weight, eating disorders such as anorexia and bulimia, and over exercising, especially in female athletes, are read as stress factors by the body and affect hormone levels, causing a missed menstrual period.
Menopause
The levels of estrogen and progesterone which are produced in the ovaries decrease as a woman reaches her late thirties. Perimenopause is the time leading up to menopause and lasts from two years to eight years. During this phase, estrogen and progesterone levels are irregular and missed menstrual periods are a symptom. A woman reaches menopause one year after having her last menstrual period.
