Thyroid and Menstruation

In healthy women, the menstrual cycle is simply an accepted fact of life, a monthly event that sometimes brings on temporary mood swings, fatigue, and cravings for high-fat foods. But many women endure monthly challenges with their menstrual cycle. They may have periods that are heavy, irregular, or extremely painful. In some women, their periods are fine for years, and then suddenly become problematic.

When something is irregular with the menstrual cycle, most women don't look to their thyroid as the culprit. Instead, they may blame stress, a recent illness, or advancing age. They may think they're having early signs of menopause. But often, the real reason for their menstrual problems is their thyroid.


In the United States, the average age a girl starts menstruating is 12, but it can start as early as eight or as late as 16. On average, menstruation will stop and menopause will occur when a woman is around age 51.

The Inner Workings of Menstruation

Menstruation is a monthly event that prepares a woman for pregnancy. In the first half of the menstrual cycle, levels of estrogen rise, causing the lining of the uterus to grow and thicken. The rise in estrogen is followed by an increase in FSH, which triggers an egg, or ovum, in one of the ovaries to start to mature. At about day 14 of a typical 28-day cycle, there is a surge in LH, and the egg leaves the ovary, an event known as ovulation.

During the second half of the menstrual cycle, the egg travels through the fallopian tube to the uterus in anticipation of fertilization. In preparation, progesterone levels rise to help prepare the uterine lining for pregnancy. If the egg becomes fertilized by a sperm cell and attaches itself to the uterine wall, the woman becomes pregnant.

But most times, the egg is not fertilized, and simply dissolves or is absorbed into the body. If pregnancy does not occur, estrogen and progesterone levels drop, and the thickened uterine lining is shed during the menstrual period.

The Thyroid Impact

No one knows exactly how the thyroid hormones influence a woman's monthly cycle, but in women with thyroid disease, the monthly menstrual cycle can be significantly altered or disrupted. A thyroid problem can also affect teenage girls. Girls who get their period very early — before the age of 10 — may be suffering from an overactive thyroid. Those who are 15 or older when they get their first period may have hypothyroidism.

In women who have hypothyroidism, it's not uncommon for their periods to become much heavier than before. The duration of their periods may also increase, or they may notice that their cycle has gotten shorter, and they're getting their periods more frequently.

According to one study, approximately 23 percent of women with hypothyroidism experience menstrual irregularities. Other estimates have found that the impact is significantly higher.

The problems are different in women who have hyperthyroidism. Women whose thyroids are overactive tend to experience lighter periods, less frequent periods, or even complete absence of their monthly cycles. Approximately 22 percent of hyperthyroid women have menstrual problems, though again, some estimates suggest the rate is much higher. The most common disturbances are defined as:

  • Amenorrhea

    Amenorrhea is the medical term for the lack of menstrual periods. In women who have been menstruating, it is called secondary amenorrhea and defined by the absence of periods for more than three to six months. It is also diagnosed in girls who have not had their first periods by the age of 16 and is called primary amenorrhea.

  • Oligomenorrhea

    When a woman has fewer than six to eight menstrual periods in a year, she may be diagnosed with oligomenorrhea, or infrequent periods. While some women may celebrate the fact that their periods have become less frequent, diminished frequency is usually a sign of a potential medical problem such as thyroid disease.

  • Dysmenorrhea

    In some women, hypothyroidism can cause painful menstrual periods, known as dysmenorrhea. Dysmenorrhea can also involve lower back pain, nausea, bowel problems, achiness in the lower extremities, and excessive bloating.

  • Menorrhagia

    Extremely heavy or prolonged menstrual bleeding is called menorrhagia. Women with menorrhagia may need to change their sanitary pad every hour over the period of several hours.

  • Shortened Cycles

    Some women with hypothyroidism will notice that their menstrual cycle shortens by a few days. They may also have bleeding that lasts longer.

Call the Doctor

It's not unusual for healthy women to sometimes skip a period, have a delayed period, or experience changes in the heaviness of their flow. But some signs warrant medical attention. You should call your doctor if you:

  • Have periods that occur less than 21 days apart

  • Have not had a period for more than three months

  • Are experiencing greater pain with your periods

  • Bleed heavily for more than 72 hours

  • Have periods that routinely last more than a week

  • Get your period at age eight or nine

  • Do not get your period until age 16 or older

When trying to determine the cause of your menstrual irregularities, your doctor should consider many factors, including your thyroid. He should ask you about your personal and family history; medications you are taking; recent stress; and changes in your diet, exercise, and weight.

He should ask about other signs and symptoms. A problem with your hypothalamus or pituitary, for example, may be accompanied by headache or vision problems. Significant weight loss may be a sign of anorexia or bulimia. The presence of hot flashes may suggest the onset of menopause.

If hypothyroidism is at the root of your menstrual irregularities, proper treatment usually corrects the disturbance. But the key, again, is establishing the right dose, so that you are at the right TSH level. The same is true if you are experiencing hyperthyroidism — you must strive to be at your optimal TSH level. If you are at the right TSH level but are still experiencing menstrual problems, you may need to consult with an endocrinologist who specializes in reproductive disorders.

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