The thyroid gland is an important gland that plays a major role in your reproductive system and health. Shaped like a butterfly and located at the front (and base) of your neck, the thyroid is a small-hormone producing organ that directly affects the ovaries and indirectly interacts with sex hormone-binding globulin (SHBG), a protein that binds sex hormones. The thyroid also regulates a plethora of the body’s functions such as your metabolism, body temperature, and heart rate. Depending on how much excess or how little hormone your thyroid makes, may make you feel restless or tired, or lose or gain weight.

When your thyroid is dysfunctional (not producing enough hormones), it can result in slowing down the body’s functions thus causing irregularities with your menstrual cycle. Two main hormones that the thyroid produces are T4 (thyroxine) and T3 (triiodothyronine), and when hypothyroidism occurs, it is due to your thyroid, producing an insufficient amount of these hormones, thus making it underactive. Its opposite, hyperthyroidism, is when an excess amount of thyroid hormone is being produced. Both can cause amenorrhea, an absent period, or oligomenorrhea, an infrequent period.

If you have an iodine deficiency, autoimmune disease, or physical damage to the thyroid, it could cause hypothyroidism. In some cases, pregnancy can cause postpartum thryoiditis, which usually begins between 2-6 months after birth. Hyperthyroidism during pregnancy may also increase your risk of miscarriages.

Symptoms associated with menstrual irregularities include heavy, frequent bleeding or an infrequent/absent period, which is a more common symptom. When you’re experiencing absent or infrequent periods (from hypothyroidism), it is due to an increase of the thyroid releasing hormone (TRH). High TRH levels will trigger the release of prolactin, located near the pituitary gland, thinning the uterine lining and interfering with the production of estrogen. This can also cause infertility and an abnormal discharge of a milky substance from the breasts. If your immune system causes thyroid disease, you could possibly enter menopause early (before 40), which is could be linked to hyperthyroidism. Hypothyroidism is more than likely to occur after menopause. You could also possibly mistake your symptoms of the thyroid for menopause symptoms.

If you are experiencing amenorrhea or oligomenorrhea, talk to your doctor and asked for your thyroid levels to be checked. It could be a clue to why your period is not operating normally.