A woman’s menstrual cycle can say a lot about her. A monthly menstrual cycle indicates she is healthy and her hormones are probably within normal levels. For the most part, a menstrual cycle will occur every 21 to 35 days, although the frequency can change a bit through the reproductive years. To understand how and why these changes occur, it is important to understand how the menstrual cycle works.
The Menstrual Cycle: How It Works
Biologically, a woman’s body is set up to reproduce. Each month, while she is fertile, a series of precise hormonal changes will occur to prepare her body for the possibility of conception and pregnancy:
1. In the first half of a woman’s menstrual cycle, the pituitary gland in the brain produces a signaling chemical, or hormone, called FSH, which tells the ovaries to make estrogen—a lot of it.
2. When the estrogen reaches a set level for a specific length of time, the pituitary produces another hormone, LH.
3. LH triggers ovulation, with the the ovary releasing an egg to be picked up by the fallopian tube.
4. The ovary then starts to produce a lot of progesterone, which prepares the uterus for pregnancy.
5. If conception occurs, the developing pregnancy will start to make progesterone. If it doesn’t occur, the level of hormones drop and, without progesterone, the menstrual lining stops developing and is “shed”—what a woman experiences as a menstrual period.
For all these events to happen, the levels of hormones must be precisely right. If a woman is having regular menstrual cycles, her hormones most likely are all normal. Testing levels of hormones in these women is usually unnecessary.
The Early Years
In a woman’s early adolescent years, her cycle may not be regular. It usually takes a year or so until the pituitary gland and ovaries have learned how to work together to produce regular levels of hormones. Many women may not ovulate the first few times they have a menstrual cycle. Adolescence is a time of rapidly changing hormonal levels and it can take a few years until the cycle becomes regular.
After Adolescence
After adolescence, a woman’s cycle should be between 21 and 35 days, with her period lasting 3 to 7 days. If she is not menstruating on a regular basis, it could be a sign of hormonal imbalances and she should talk to her doctor about it.
Mid-Life Changes
In her mid- to late 40s, a woman’s cycle can become irregular again. Women are born with all the eggs they will have; when the eggs run out, menopause occurs. During the transition to menopause (the perimenopausal phase), the remaining eggs tend to not be as good or “robust,” and they make less estrogen. If estrogen levels drop early, the pituitary gland will produce more FSH (this is the hormone that is checked in fertility tests). With higher FSH levels, ovulation is triggered earlier and a woman’s menstrual cycle can shorten. It is not unusual for her menstrual cycle to condense to 21 days during the late 40s. Skipped cycles are not uncommon as women stop ovulating.
The Bottom Line
The bottom line is that a regular menstrual cycle of 21 to 35 days signals that a woman’s hormones are in good balance. Lack of regular cycles, except at the very beginning and at the end of the reproductive years, may indicate problems and is a reason to seek the advice of a gynecologist.
To find an excellent gynecologist who is right for you, please call our Physician Referral Service at 866.804.1007.