How Thyroid Function Affects Menstruation

The thyroid gland is a small butterfly-shaped gland located at the base of the front of your neck. It plays an essential role in your reproductive health, directly affecting your ovaries and indirectly interacting with sex hormone-binding globulin (SHBG), a protein that "sticks" to reproductive hormones so they can be carried throughout your body.

Given this, thyroid dysfunction can result in menstrual irregularities. However, menstrual problems tend to be more common in those with severe thyroid disease versus those with more mild or moderate cases.

This article explains why and 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
• Frequent menstrual bleeding
• Infrequent cycles
• Absent menstrual cycles

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. Too much thyroid hormone leads to increased SHBG, which can prevent ovulation.
• 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 prevent 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 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
  

Decreased Fertility

Since a lack of thyroid hormone can prevent ovulation, having hypothyroidism can make it difficult to get pregnant. Moreover, people with hypothyroidism who are pregnant have an increased risk of miscarrying during the first trimester.

The upside is that treatment with thyroid hormone replacement medication (levothyroxine) may improve fertility and lower the risk of pregnancy loss. That said, some people who use thyroid medication continue to experience abnormal periods.

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.