Hormonal Regulation of Menstruation
Adapted from Menstrual Bleeding: A Healthy and Necessary Function in Women’s Health
A Connections publication of Women’s International Pharmacy
Menstruation is the phase of the female reproductive cycle in which the body sheds the uterine lining (endometrium) if pregnancy does not occur. Menstrual bleeding cleanses the uterus, preparing it for the next reproductive cycle. Due to hormonal changes during certain phases in a woman’s life, irregularities in the menstrual cycle are fairly common, and many may be addressed by first bringing her hormone levels back into balance.
The buildup and shedding of the endometrium are controlled by hormonal fluctuations, primarily in the estrogens and progesterone. These fluctuations are the result of an elaborate feedback system among different parts of the brain, ovaries, and uterus. The hypothalamus, the pituitary, and the ovaries are the glands that produce hormones directly involved in triggering different phases of the menstrual cycle. Other glands, including the thyroid and adrenal glands, also affect menstruation.
According to Dr. Susan 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. It signals the pituitary gland 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 signals the endometrium to gradually rebuild itself by increasing the number of blood vessels and forming a fiber mesh that thickens the uterine lining. The pituitary releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which target the ovaries. The ovaries begin ovulation upon receiving this signal.
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 is 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 mucus 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 in the Menstrual Cycle
Menstrual regularity is primarily determined by a complex interaction between the brain, ovaries, and uterus. The brain’s hypothalamus is so sensitive to stress that any form of stress may hinder its ability to pass signals to the pituitary. The resulting hormonal imbalance 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.
During life phases such as puberty and perimenopause, irregular bleeding is usually caused by insufficient levels of the estrogen hormones, resulting in no ovulation. The lack of ovulation means that there is no progesterone production during the second half of the menstrual cycle, resulting in no bleeding, spotting, or irregular bleeding patterns.
Heavy Menstrual Bleeding
Heavy menstrual bleeding includes bleeding that is either too heavy or too fast, or moderate bleeding that occurs for an extended time. Large blood clots and mid-cycle spotting may also occur. Common causes may include:
- Estrogen dominance
- Nutritional deficiencies
- Ovarian cysts
- Uterine fibroids
No Menstrual Bleeding
Amenorrhea is the lack of menstrual bleeding and is divided into two types: primary amenorrhea and secondary amenorrhea. Primary amenorrhea refers to a woman who is past puberty but has never experienced menstrual bleeding. Common causes include hormonal imbalance or congenital abnormalities of the vagina, uterus, or ovaries.
Secondary amenorrhea is more prevalent than primary amenorrhea and refers to the condition when a woman stops menstruating after experiencing regular periods. The most common reason for missing a period is pregnancy. Other potential reasons involve factors that may disrupt the hormone balance necessary to maintain a regular bleeding cycle:
- Emotional trauma
- Weight gain or loss
- Poor nutrition
- Excessive exercise
- Prolonged use of birth control pills
Hormone Therapies for Abnormal Bleeding
Depending on the underlying cause, various forms of abnormal bleeding may often be treated to induce menses, regulate flow, and/or alleviate symptoms. Hormonal replacement therapies are often prescribed to regulate the cycle and reduce blood flow.
Progesterone helps prevent erratic periods and heavy bleeding and is sometimes combined with estrogen hormones, depending on the reason for the abnormal bleeding. Research indicates that progesterone therapy is effective in treating irregular bleeding, especially for women in perimenopause. Dr. Lark agrees that progesterone is “the most effective medical treatment available for women in menopause transition.”
Thyroid therapy is often prescribed because low thyroid function is a common cause of heavy menstrual bleeding. Women account for almost 90% of the hypothyroidism cases in the United States. Replenishing thyroid hormone levels may be used to correct this imbalance, resolving the root cause of the abnormal bleeding.
Different stages of a woman’s life are usually accompanied by changes in her menstrual cycle. Periods may be irregular during puberty while a young woman’s body adjusts to balance the hormonal influx and may become irregular again leading up to menopause, reflecting the change in a woman’s hormone balance as various hormone levels decrease. No matter what stage of life a woman is in, her menstrual and overall health may be optimized by identifying hormone imbalance and finding a personalized treatment plan to bring them into equilibrium.
Not all forms of hormone therapy are equally effective. There are significant differences between “conventional” synthetic hormone therapies and “natural” hormone therapies that use bioidentical hormones. Bioidentical hormone therapies are beneficial not only because they use hormones that are identical to those produced by the human body, but they may also be custom-compounded to fit each patient’s individual needs.
- Fitzpatrick LA, Good A. Micronized progesterone: clinical indications and comparison with current treatments. Fertil Steril. 1999 Sep;72(3):389-97.
- Lark S. Heavy Menstrual Flow & Anemia Self Help Book. Third Ed. Berkeley, CA: Celestial Arts; 1999.
- McCormick K. Feminine Bleeding: What’s “Normal”? Connections. Women’s International Pharmacy, 2005.