Once a woman starts menstruating, she should expect to have a period every month or so. However, each woman's body, and therefore period timing, is unique. Once a woman is having regular periods, however, it is not normal to go six months between menstrual cycles. Consult your doctor for medical advice.
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A primary physiologic cause of amenorrhea is pregnancy. If a woman of childbearing age has not had a period for six months, a pregnancy test is warranted. (AHRQ,ref 3) Other physiologic causes include lactation, especially in the first six months after birth. Menopausal women will become amenorrheic over time. It is important to note if a woman is experiencing other symptoms that indicate menopause, such as hot flashes. (FP notebook)
Many contraceptives can cause amenorrhea.(FP notebook) The birth control injection depot medroxyprogesterone acetate (Depo Provera), the Mirena intrauterine system, and the Skyla intrauterine system may cause amenorrhea as well. The birth control implant Nexplanon may also cause amenorrhea. Certain birth control pills, such as progesterone only birth control pills, can cause amenorrhea. In addition, continuous cycling of combined oral contraceptive pills can cause a woman to skip periods for six months or longer, depending on if she opts to not take the placebo pills.
Hormonal abnormalities can cause a woman to miss her periods for six months or longer. High prolactin levels and low thyroid levels are common causes. Medical conditions such as Sheehan Syndrome, sarcoidosis, and Cushing Syndrome are less common causes. Polycystic ovarian syndrome, a group of symptoms including obesity, hirsutism, and insulin resistance, is an increasingly common cause of amenorrhea. (ref 2)
In addition to hormonal aberrations that cause amenorrhea, other pathological causes include anorexia cervical stenosis, and endometritis. If a woman is significantly underweight or overweight, she may miss her periods. Prolonged amenorrhea increases a woman's risk for endometrial hyperplasia and endometrial cancer, or cancer within the uterus. It is essential that a woman with amenorrhea see her doctor for work-up and treatment. (fp notebook)