How Your Thyroid Function Affects Menstruation

If you are experiencing unusual symptoms around your menstrual cycle, your thyroid may be the culprit.

The thyroid gland, a small butterfly-shaped gland located at the base of the front of your neck, plays an important role in your reproductive health, directly affecting your ovaries and indirectly interacting with sex-hormone binding globulin (a protein that binds sex hormones).

With the link between your thyroid and your reproductive organs and hormones, it's a given that thyroid dysfunction may result in menstrual irregularities—although, menstrual problems tend to be more common in those with severe thyroid disease versus those with mild or moderate thyroid disease.

Let's take a closer look at the thyroid and menstruation link, and what you can do to address it with your doctor.

Hypothyroidism, or an underactive thyroid gland, is a disorder of insufficient thyroid hormone production.

There are a number of menstrual irregularities associated with hypothyroidism, ranging from heavy, frequent menstrual bleeding to infrequent, or even absent, menstrual cycles.

Heavy Menstruation

According to the American College of Obstetrics and Gynecologists, heavy menstrual bleeding is defined by one or more of the following features:

• 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 as a quarter or larger.

Keep in mind, while hypothyroidism is one potential cause of heavy menstrual bleeding, there are many other potential diagnoses, including fibroids, polycystic ovarian syndrome, medication side effects, uterine cancer, and infection, among others.

Be sure to see your gynecologist if you are experiencing excessive menstrual bleeding. Tests like a pelvic examination, transvaginal ultrasound, and blood work, including a thyroid stimulating hormone (TSH) test, can help your doctor make a diagnosis.

Absent or Infrequent Menstruation

On the opposite end of the spectrum from heavy menstruation, absent menses (amenorrhea) or infrequent menses (oligomenorrhea) may occur with hypothyroidism. Infrequent menses are more common.

Amenorrhea or oligomenorrhea can occur from the increase in thyroid releasing hormone (TRH) in women with hypothyroidism. The high TRH levels trigger the release of prolactin by the pituitary gland (a pea-sized organ located at the base of the brain).

Prolactin interferes with the production of estrogen from the ovaries, causing infrequent or absent periods, as well as other potential symptoms like infertility, an abnormal milky discharge from the breasts (called galactorrhea), and symptoms of menopause, such as hot flashes and vaginal dryness.

Decreased Fertility

Menstrual irregularities can make it difficult to get pregnant. Moreover, women with hypothyroidism who are pregnant have an increased risk for miscarrying during the first trimester.

The upside here is that treatment of hypothyroidism with thyroid hormone replacement medication (levothyroxine) may correct infertility and decrease the risk of pregnancy loss. That said, some women with hypothyroidism continue to experience abnormal menstrual cycles, despite thyroid medication.

A disorder of an overactive thyroid gland, meaning there is excessive thyroid hormone being produced, is called hyperthyroidism.

Absent or infrequent menses are the most common abnormalities seen with severe hyperthyroidism. This is because an increase in thyroid hormone indirectly causes an increase in sex hormone-binding globulin (SHBG), which can prevent ovulation.

As with hypothyroidism, an overactive thyroid gland that leads to scant or missed periods decreases fertility. In addition, thyrotoxicosis during pregnancy increases the risk of miscarriage, which is why treatment with an anti-thyroid drug monitored and prescribed by an endocrinologist is important.

While a change in your menstrual cycle may be the first clue to a thyroid disorder, be sure to contact your doctor for a comprehensive workup, as there are many other potential causes. Pregnancy, for example, should be ruled out first and foremost in the event of a missed period.

Keep in mind that the more severe your thyroid disease is, the more likely you are to experience menstrual irregularities. In other words, having normal cycles certainly does not rule out a thyroid problem and vice versa. Abnormal menstruation is a potential clue, but most definitely not a slam dunk indicator of an underlying thyroid problem.