Thyroid function is vital for a healthy reproductive system. The thyroid is a small, butterfly-shaped gland located at the base of your neck. It is an endocrine gland meaning its function is to produce and release hormones which are thyroxine (T4) and triiodothyronine (T3). Two glands in the brain—the hypothalamus and the pituitary gland communicate with each other and the thyroid gland to maintain T3 and T4 balance.

Female sex hormones are altered due to an underactive thyroid known as hypothyroidism which can be another possible cause of irregular or heavy periods. Hypothyroidism is greatly underdiagnosed as a cause of menorrhagia (which is the medical term for menstrual periods with abnormally heavy or prolonged bleeding).

How can an underactive thyroid cause heavy periods? When you have low thyroid function the following can occur:⠀⠀⠀⠀⠀⠀⠀⠀⠀
– your ovaries may not be able to make enough of the progesterone.⠀⠀⠀⠀⠀⠀⠀⠀⠀
– you make less of the estrogen-binding protein SHBG resulting in estrogen dominance.

Thyroid function and Menstruation⠀⠀⠀⠀⠀⠀⠀⠀⠀
One study showed that over 20% of women with hypothyroidism had some type of irregular period, especially heavy periods or infrequent periods. Hypothyroidism has also been associated with an absence of any period for more than three cycles.

Thyroid function and Infertility ⠀⠀⠀⠀⠀⠀⠀⠀⠀
Women who have trouble falling pregnant must consider checking their thyroid function. Hypothyroidism can affect fertility in several ways, including preventing normal ovulation, which can cause irregular menstrual cycles, and increasing the risk of miscarriage. One study found that over 75% of women who had difficulty conceiving conceived within a year of starting thyroid treatment. It’s worth noting that very mild hypothyroidism (without any obvious symptoms) can interfere with normal reproduction, so it’s common for providers to check thyroid levels if you’re trying to conceive.