Women experience missed or delayed menstrual periods for a variety of reasons ranging from pregnancy to sudden weight loss or gain. According to WebMD, women in the midst of perimenopause, a biological stage leading up to menopause, often experience delayed menstrual periods.
The parenting and pregnancy information website What to Expect explains that the reasons for a delayed period include anything that affects the body's fat cells. Women who suddenly lose or gain weight often experience amenorrhea, another term for a late menstrual period. This is because women who lose a great deal of weight often do not have enough healthy fat cells to generate estrogen, while women who gain significant weight frequently experience disruptions to normal hormone function.
Other causes of a late period, according to What to Expect, include eating disorders, stress and excessive exercise, all of which are capable of disrupting normal hormone function. Women with under-active thyroid glands sometimes experience disruptions to their bodies' production of prolactin, a hormone required for ovulation and normal menstrual function. Certain medications, such as anti-depressants and corticosteroids, also frequently affect the menstrual cycle leading to delayed periods. Women with hormone imbalances caused by conditions such as polycystic ovarian syndrome, or PCOS, often skip periods altogether.
WebMD urges women not to jump to conclusions when their periods are late and to consult a doctor if they are concerned.