Amenorrhea: Causes

Secondary amenorrhea
Secondary amenorrhea is much more common than primary amenorrhea. Many possible causes of secondary amenorrhea exist:

• Pregnancy. In women of reproductive age, pregnancy is the most common cause of amenorrhea. When a fertilized egg is implanted in the lining of your uterus, the lining remains to nourish the fetus and isn't shed as menstruation.
• Contraceptives. Some women who take birth control pills may not have periods. When oral contraceptives are stopped, it may take three to six months to resume regular ovulation and menstruation. Contraceptives that are injected or implanted, such as Depo-Provera, also may cause amenorrhea as can progesterone-containing intrauterine devices, such as Mirena.
• Breast-feeding. Mothers who breast-feed often experience amenorrhea. Although ovulation may occur, menstruation may not. Pregnancy can result despite the lack of menstruation.
• Stress. Mental stress can temporarily alter the functioning of your hypothalamus — an area of your brain that controls the hormones that regulate your menstrual cycle. Ovulation and menstruation may stop as a result. Regular menstrual periods usually resume after your stress decreases.
• Medication. Certain medications can cause menstrual periods to stop. For example, antidepressants, antipsychotics, some chemotherapy drugs and oral corticosteroids can cause amenorrhea.
• Illness. Chronic illness may postpone menstrual periods. As you recover, menstruation typically resumes.
• Hormonal imbalance. A common cause of amenorrhea or irregular periods is polycystic ovary syndrome (PCOS). This condition causes relatively high and sustained levels of estrogen and androgen, a male hormone, rather than the fluctuating levels seen in the normal menstrual cycle. This results in a decrease in the pituitary hormones that lead to ovulation and menstruation. PCOS is associated with obesity; amenorrhea or abnormal, often heavy uterine bleeding; acne and sometimes excess facial hair.
• Low body weight. Excessively low body weight interrupts many hormonal functions in your body, potentially halting ovulation. Women who have an eating disorder, such as anorexia or bulimia, often stop having periods because of these abnormal hormonal changes.
• Excessive exercise. Women who participate in sports that require rigorous training, such as ballet, long-distance running or gymnastics, may find their menstrual cycle interrupted. Several factors combine to contribute to the loss of periods in athletes, including low body fat, stress and high energy expenditure.
• Thyroid malfunction. An underactive thyroid gland (hypothyroidism) commonly causes menstrual irregularities, including amenorrhea. Thyroid disorders can also cause an increase or decrease in the production of prolactin — a reproductive hormone generated by your pituitary gland. An altered prolactin level can affect your hypothalamus and disrupt your menstrual cycle.
• Pituitary tumor. A noncancerous (benign) tumor in your pituitary gland (adenoma or prolactinoma) can cause an overproduction of prolactin. Excess prolactin can interfere with the regulation of menstruation. This type of tumor is treatable with medication, but it sometimes requires surgery.
• Uterine scarring. Asherman's syndrome, a condition in which scar tissue builds up in the lining of the uterus, can sometimes occur after uterine procedures, such as a dilation and curettage (D and C), Caesarean section or treatment for uterine fibroids. Uterine scarring prevents the normal buildup and shedding of the uterine lining, which can result in very light menstrual bleeding or no periods at all.
• Premature menopause. Menopause usually occurs between ages 45 and 55. If you experience menopause before age 40, it's considered premature. The lack of ovarian function associated with menopause decreases the amount of circulating estrogen in your body, which in turn thins your uterine lining (endometrium) and brings an end to your menstrual periods. Premature menopause may result from genetic factors or autoimmune disease, but often no cause can be found.