Menstrual bleeding is a normal, healthy, and cleansing process. However, one concern expressed by many women is that they don’t know what is “normal” when they experience menstrual bleeding. Understanding how and why menstruation occurs helps clarify what is “normal” versus “abnormal” bleeding. This will help determine what is “normal” for you, making it easier to notice irregularities and identify what has disrupted the normal bleeding pattern.
The Process of Menstruation
Menstruation is the phase of the female reproductive cycle in which the body sheds the uterine lining (endometrium) if pregnancy does not occur. Cyclical uterine shedding (i.e., menstrual bleeding) cleanses the uterus, preparing it for the next reproductive cycle. In Heavy Menstrual Flow & Anemia, Dr. Susan Lark explains menstruation as:
Each month the uterus prepares a thick, blood-rich cushion to nourish and house a fertilized egg. If conception occurs, the endometrium becomes the placenta. If pregnancy does not occur, the egg doesn’t implant in the uterus and the body doesn’t need the extra buildup of the uterine lining. The uterus cleanses itself by releasing the extra blood and tissue so that the buildup can recur the following month.
Hormones Regulate the Menstrual Cycle
The buildup and shedding of the uterine lining are controlled by fluctuations in hormones, primarily the estrogens and progesterone. These hormonal fluctuations are the result of an elaborate feedback system among different parts of the brain, ovaries, and uterus. The glands that produce the hormones that are directly involved in triggering the different phases of the menstrual cycle are the hypothalamus, the pituitary, and the ovaries; other glands, including the thyroid and adrenal glands, also affect menstruation.
According to Dr. Lark, “The initial trigger for the menstrual cycle comes from hormones produced by the hypothalamus.” The hypothalamus is a gland just above the pituitary near the base of the brain and regulates many basic bodily functions, including hunger, thirst, body temperature, and sleep patterns. It also signals the pituitary to begin producing hormones, which stimulates all other glands in the body, including the ovaries, adrenal glands, and thyroid.
During the first two weeks of a normal cycle (immediately following the previous menstruation), estrogen triggers the endometrium to gradually rebuild itself by increasing the number of blood vessels and forming an interconnecting fiber mesh that thickens the uterine lining. The pituitary releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which target the ovaries. Upon receiving this signal (usually mid-cycle), the ovaries begin ovulation.
At this point, the follicles begin producing more of the estrogens (as well as some progesterone), which triggers the ripening and release of an egg for potential fertilization as it travels down the fallopian tube to the uterus. The follicle that produced that month’s egg becomes further stimulated by LH and transforms into the corpus luteum, which secretes more progesterone, triggering the uterine lining blood vessels to coil, and becoming swollen and thick with mucous in preparation for a fertilized egg. If fertilization occurs, the egg implants on the uterine wall and the corpus luteum continues secreting progesterone. If fertilization does not occur, progesterone levels decrease, triggering the corpus luteum and uterine lining to break down, and menstruation begins.
Sufficient levels of progesterone and the estrogen hormones are needed to maintain a healthy, regular bleeding cycle. One of the estrogen hormones, estradiol, reaches its peak during the first half of the cycle, while progesterone peaks after mid-cycle when ovulation has occurred. The timing of those peaks is one aspect of regulating the menstrual cycle.
Variations of “Normal”
Most women are taught that the “normal” menstrual cycle is 28 days with three to five days of bleeding. However, Dr. Christiane Northrup believes that description of “normal” is too narrow, finding that typical cycles range anywhere from 24 to 35 days and that bleeding duration also varies. Dr. Hyla Cass agrees, noting that “most women’s periods last two to seven days.”
Rates of flow also vary considerably; what one woman considers a heavy flow is light for another. Given the wide variations of a “normal” cycle, it is important to determine what is normal for you by paying attention to your menstrual patterns and flow, so that you may more easily identify when potentially significant changes occur. Menstrual changes other than timing and flow may be significant when describing “normal” menstrual cycle:
- Some women observe a clear discharge similar to raw egg white approximately 12 to 16 days after the first day of their last menstrual period (sometimes referred to as “fertile flow” because it usually indicates ovulation has occurred)
- Some women notice a distinct odor that occurs only during menstruation, often as a result of increased sweating in the pubic area
- Many women report periodic spotting (light bleeding between cycles or instead of cycles) or clotting (shedding thick or stringy blood clots)
Variations in the menstrual cycle often coincide with different stages of a woman’s life. A young woman’s periods may be irregular during puberty while her body adjusts to balance the hormonal influx. A woman’s periods may become irregular again leading up to menopause, reflecting the change in her hormone balance as various hormone levels decrease.
Determining what is normal requires looking at the bigger picture—the context of your life—not just the timing of your last menstrual cycle. Bleeding patterns may be disrupted by changes in:
- Exercise levels
- Family or emotional stress
Sometimes an irregularity in the menstrual cycle is a normal reaction to an abnormal situation, such as illness or the death of a loved one.
Menstrual regularity is primarily determined by a complex interaction between the brain (hypothalamus, pituitary gland, and temporal lobes), the ovaries, and the uterus. The hypothalamus is so sensitive to stress that any form of stress may hinder its ability to pass signals to the pituitary. The resulting imbalance of hormones disrupts the menstrual cycle, altering the bleeding pattern or flow.
Anything that impairs liver function may also disrupt menstrual patterns because the liver is responsible for breaking down estrogen hormones. Without proper liver function, increased levels of estrogens may thicken the uterine lining and contribute to heavier bleeding. Factors that affect liver function include cigarette smoking, excessive alcohol consumption, and poor nutritional habits.
Common Menstrual Irregularities
Abnormal bleeding may result from many different situations and conditions, some of which are unrelated to ovulation or menstruation. For example, unexpected bleeding may occur soon after stopping birth control pills. Abnormal bleeding may also signal a potential miscarriage or an ectopic pregnancy, or indicate the presence of a cyst, polyp, or fibroid tumors.