Amenorrhea, the absence of menstruation, can happen for many different reasons. Firstly, there’s primary amenorrhea, in which a female has not had even her first cycle by age 16. Secondly, there’s secondary amenorrhea, where the female normally has a cycle, but then for some reason starts missing periods. It is important to remember that amenorrhea is not considered a disease; it is a symptom.
So what causes it?
In primary amenorrhea, the Mayo Clinic list five different causes as indicated below:
Chromosomal abnormalities - Certain chromosomal abnormalities can cause a premature depletion of the eggs and follicles involved in ovulation and menstruation.
Problems with the hypothalamus - Functional hypothalamic amenorrhea is a disorder of the hypothalamus — an area at the base of your brain that acts as a control center for your body and regulates your menstrual cycle. Excessive exercise, eating disorders, such as anorexia, and physical or psychological stress can all contribute to a disruption in the normal function of the hypothalamus. Less commonly, a tumor may prevent your hypothalamus from functioning normally.
Pituitary disease - The pituitary is another gland in the brain that's involved in regulating the menstrual cycle. A tumor or other invasive growth may disrupt the pituitary gland's ability to perform this function.
Lack of reproductive organs - Sometimes problems arise during fetal development that lead to a girl being born without some major part of her reproductive system, such as her uterus, cervix or vagina. Because her reproductive system didn't develop normally, she won't have menstrual cycles.
Structural abnormality of the vagina - An obstruction of the vagina may prevent visible menstrual bleeding. A membrane or wall may be present in the vagina that blocks the outflow of blood from the uterus and cervix.
In regards to secondary amenorrhea, the Mayo Clinic lists 12 reasons why a woman may start to miss periods:
Pregnancy - In women of reproductive age, pregnancy is the most common cause of amenorrhea.