Most women will experience an irregular menstrual cycle at some point in their reproductive years. Missing a menstrual period can be due to stress or hormonal imbalances in the beginning of puberty, as well as hormonal imbalances leading up to menopause. However, there are other conditions that can affect the reproductive system and cause skipped menstrual cycles.
Menopause
Menopause is a condition that marks the end of a woman's reproductive years. According to MedlinePlus, this usually occurs between the ages of 45 and 55. During menopause, a woman fails to ovulate or menstruate due to a natural decline in the hormone estrogen.
In a normal monthly cycle, estrogen, produced by the ovaries, receives a message from the pituitary gland to spike and begin the fertilization process. Estrogen, along with the female hormone progesterone, work together to produce an egg and thicken the uterine lining to support the egg once it's fertilized. The hormone levels stay steady once the egg is fertilized to stop menstruation from happening, but if the egg is not fertilized these levels lower again to start menstruation.
Estrogen levels begin to lower more and more after the age 30, according to "Mayo Clinic Family Health, Third Edition," until menopause when estrogen levels are so low that the menstrual cycle stops altogether. Although some women may only have missed menstrual cycles as a symptom, other women experience hot flashes, vaginal dryness, mood swings or insomnia.
Pregnancy
Often the first sign of pregnancy is a missed period. Roughly five days into the pregnancy, the egg goes into what's known as the blastocyst stage. In this stage, the egg connects to the uterine lining, where it will remain for nine months. Once it attaches to the uterine lining, the fertilized egg forms a hormone called Human Chorionic Gonadotrophin, or HCG. The production of HCG sends a signal to the ovaries to keep the same level of estrogen, so that menstrual cycles do not occur.
Polycystic Ovary Syndrome
Polycystic ovary syndrome, or PCOS, is a condition that causes the ovaries to produce many cysts. PCOS also causes a woman to gain weight, grow facial hair and have unpredictable menstrual cycles. Some women with PCOS have heavy menstrual cycles, others may have prolonged menstrual cycles or may miss their menstrual cycle altogether.
Researchers are not sure of what exactly causes PCOS, however they do speculate that the hormonal imbalance in PCOS is caused by an over-production of the luteinizing hormone, secreted from the pituitary gland. When luteinizing hormone is released it normally sends a signal to the ovaries to produce a certain amount of estrogen. This amount is enough to form a cyst within the ovary. Within the cyst, an egg is formed and matured, and is then released from the cyst when the estrogen level surges. In women with PCOS, the luteinizing hormone secretes at a high level causing the level of estrogen to fluctuate. This causes the egg inside to remain immature, so the cyst doesn't open; this causes a lack of ovulation and irregular menses.
