How Thyroid Function Affects Menstruation

Thyroid problems can result in menstrual irregularities. This is because the thyroid gland, a small butterfly-shaped gland located at the base of the front of your neck, plays an essential role in your reproductive health.

The thyroid directly affects your ovaries and indirectly interacts with sex hormone-binding globulin (SHBG). SHBG is a protein that "sticks" to reproductive hormones so they can be carried throughout your body.

Menstrual problems tend to be most common in those with severe thyroid disease and less common in those with more mild or moderate cases.

This article explains why thyroid disorders can cause menstrual irregularities. It also covers some of the most common menstrual symptoms related to thyroid disorders, plus what you can do about them.

Hypothyroidism vs. Hyperthyroidism

Problems with your menstrual cycle may be due to an underactive or overactive thyroid. How symptoms present could depend on which type of thyroid disorder you have.

Hypothyroidism

Hypothyroidism, or an underactive thyroid gland, occurs when the body produces too little thyroid hormone. There are several menstrual problems associated with hypothyroidism, including:

• Heavy menstrual bleeding: This is a common symptom in many people with hypothyroidism.
• Frequent menstrual bleeding: People with hypothyroidism may also have menstrual periods that last longer or occur more often than people without the condition.
• Infrequent cycles: Hypothyroidism may also cause you to miss periods or have them less often.
• Absent menstrual cycles: Some people with hypothyroidism may not menstruate.
• Infertility and miscarriage: People with untreated hypothyroidism may have trouble conceiving and are more likely to experience miscarriage and pregnancy complications.

The first-line treatment for hypothyroidism is the thyroid hormone replacement medication Levoxyl (levothyroxine). This medication has been shown to improve menstrual problems even in people with normal thyroid function. That said, some people who use thyroid medication continue to experience abnormal periods.

Hyperthyroidism

Hyperthyroidism is a disorder of an overactive thyroid gland. That means your body produces too much thyroid hormone.

Menstrual abnormalities seen with hyperthyroidism include:

• Absent or infrequent periods: This is the most common symptom seen with severe hyperthyroidism.
• Light and short periods: Bleeding may be less than typical—and brief.
• Decreased fertility: Not ovulating can impact your fertility.
• Risk of miscarriage: In addition, excessive thyroid hormone production during pregnancy increases the risk of miscarriage.

Treatment with an antithyroid drug can help regulate thyroid function and alleviate these menstrual and fertility problems.

Another option is radioactive iodine (RAI) therapy, which shrinks the thyroid. However, this treatment is not safe during pregnancy.

Heavy Menstruation

The American College of Obstetricians and Gynecologists (ACOG) defines heavy menstrual bleeding as one or more of the following:

• Bleeding that lasts more than seven days
• Bleeding that soaks through one or more tampons or pads every hour for several hours in a row
• Needing to wear more than one pad at a time to control menstrual flow
• Needing to change pads or tampons during the night
• Menstrual flow with blood clots that are as big or bigger than a quarter

Be sure to see your OB/GYN if you are experiencing heavy periods. To help with diagnosis, they may want to perform some tests such as a:

• Pelvic examination
• Transvaginal ultrasound: Imaging done by inserting a wand into the vagina so that images of your reproductive organs can be transmitted onto a monitor
• Thyroid-stimulating hormone (TSH) blood test

Absent or Infrequent Menstruation

Hypothyroidism and hyperthyroidism can also lead to absent periods (amenorrhea) or infrequent periods (oligomenorrhea). Irregular periods are more common.

Absent or infrequent cycles can occur from high thyroid releasing hormone (TRH) in people with hypothyroidism. The high TRH levels trigger the pituitary gland (a pea-sized organ located at the base of the brain) to release prolactin.

Too much prolactin interferes with the ability of the ovaries to produce estrogen. Reduced estrogen can lead to some reproductive health symptoms and issues, including:

• Infrequent periods
• Absent periods
• Abnormal milky discharge from the breasts (galactorrhea)
• Hot flashes
• Vaginal dryness
• Infertility

In people with hyperthyroidism, too much thyroid hormone leads to increased SHBG, which can prevent ovulation.

Decreased Fertility

Since a lack of thyroid hormone can prevent ovulation, having thyroid problems can make it difficult to get pregnant. Hyperthyroidism may also cause early menopause, or menopause that occurs before or around the age of 40.

Moreover, people with hypothyroidism or hyperthyroidism who are pregnant have an increased risk of miscarrying.

For people with hypothyroidism, treatment with levothyroxine may improve fertility and lower the risk of pregnancy loss.

People with hyperthyroidism are often treated with antithyroid medication during the second half of pregnancy. Because these medications cross the placenta, however, their use needs to be carefully monitored by a healthcare provider.

Summary

Thyroid conditions can have an impact on your menstrual cycles. Symptoms may range from heavy and frequent periods to irregular and absent cycles. These symptoms are due to how thyroid hormones impact reproductive hormone production.

As such, menstrual irregularities could also affect fertility and pregnancy.

A Word From Verywell

While a change in your menstrual cycle may be the first indication of a thyroid disorder, remember that there are many other potential causes. It's always best to contact your healthcare provider for an evaluation so the underlying cause can be confirmed.