Some women face abnormal periods that usually stop for 6 months or more are said to have amenorrhea or the absence of menstruation which is also known as secondary amenorrhea. Here it is worth to mention that girls who don't menstruate by the age of 16 have primary amenorrhea.

Secondary amenorrhea does not include minor lateness of a period and in case of some women, menstrual cycles of 5-6 weeks are quite normal. Stress is also a considerable factor and at times when you worry that you are or not pregnant also leads your period to be late by a week or two.

Severe emotional and physical stress or mental health problems could even cause the periods to delay or stop for a long time. Amenorrhea at a higher stage also leads to problems with the hormones that regulate menstruation. The glands that produce hormones affecting menstruation include the pituitary gland at the base of the brain, the adrenal glands on the top of the kidneys, the thyroid gland in the neck and the ovaries.

It can take a period from 6 months to a year for normal periods to resume after a woman stops taking birth control pills because the pill blocks certain hormones involved in menstruation and it can also take long for those hormones to return to normal which are involved in menstruation. Menstruation also stops during pregnancy. In case of some women, menstruation either stops or never stops because their ovaries don't respond properly to those hormones that trigger the release of an egg. These women are also unable to ovulate on their own and therefore menstruation is not possible without ovulation. Some women do not even produce enough estrogen hormones to ovulate. Other reasons of amenorrhea are ovarian cysts and obstructions or other problems in the reproductive tract.

Other factors that could cause menstruation to stop includes excessive exercise, obesity, poor nutrition, diabetes, chronic illness, tuberculosis, medications including birth control pills, narcotics, major tranquilizers and cancer chemotherapy drugs.

In some rare cases of primary amenorrhea, there is no opening in the hymen through which the blood flows and about one third of girls with primary amenorrhea have a genetic disorder or problem with their reproductive tract.