Hypothyroidism, Periods, and Fertility

Your thyroid hormones and your reproductive (sex) hormones intricately interact. Thyroid hormones affect your cycle timing, your blood flow, and your ability to conceive. (This post addresses hypothyroidism and pregnancy). Here we dive into how hypothyroidism affects your cycle and your fertility.

Follicle growth depends on thyroid hormones

Your ovaries and the oocytes (eggs) in all your follicles have high numbers of thyroid hormone receptors. When you are hypothyroid, your ovaries do not get enough thyroid hormones to ripen follicles. As a result, your follicle growth is stunted. This means ovulation may not happen, and you may:

• Experience missed, heavy, or infrequent periods.
• Have shorter cycles, with more frequent periods.
• Suffer from an overly heavy blood flow when you do have your period.

Your thyroid hormones are essential for follicle development, ovulation, and a regular healthy period.

Low thyroid hormones affects your whole cycle

More than half of hypothyroid women have menstrual irregularities. There are several scenarios that can happen to your menstrual cycle when you are hypothyroid. These are the most common:

• No ovulation: Without the right amount of thyroid hormone, your follicles will not grow and ripen as they should. If you don’t get an LH surge, which depends on thyroid hormones, you won’t ovulate.
• Short luteal phase: After ovulation, the empty follicle sac that released your egg produces progesterone. Progesterone helps you have a sufficient luteal phase (ideal is 14 days). 
• Heavy flow: Sometimes periods can be so heavy, the blood is “flooding.” This is related to low levels of progesterone.

Hypothyroidism causes other sex hormone imbalances

Estrogen Dominance

Hypothyroidism is often paired with low progesterone. It’s also frequently paired with high estrogen. This combination can also show up with PCOS (polycystic ovarian syndrome), fibroids, and endometriosis. Estrogen can be high because:

• Not enough progesterone to thin your uterine lining, and balance the estrogen
• Hypothyroidism affects your ability to metabolize and transform estrogen, so there can be a build-up.
• Hypothyroidism decreases the proteins that escort estrogen out of circulation, so this is another source of increased estrogen. These proteins are called sex hormone-binding globulin (SHBG).

Estrogen dominance symptoms include sore breasts, moodiness, bloating, headaches, PMS, and heavy flow.

High prolactin (PRL)

Frequently, hypothyroid women have high prolactin levels. Prolactin is what signals breast development and milk production during pregnancy. High prolactin lowers FSH, so follicles don’t develop well. Some women with high prolactin skip periods (amenorrhea).

Adolescent girls: delayed OR early puberty onset

Low thyroid hormones can cause delayed onset of puberty. Or, girls may menstruate early because their follicles are stimulated to ripen earlier in life.

Hypothyroidism can make it harder to conceive

Hypothyroidism can affect your ability to conceive, because of all the reasons above. About 1/3 of “subfertile” women are hypothyroid. Your TSH should be under 2.5 to conceive, as this study shows. In a nutshell:

1. If your follicles don’t mature properly, then you may not ovulate. With no egg, there’s no conception.
2. High prolactin interferes with conception.
3. If you don’t have enough progesterone, that will interfere with implantation success.
4. General menstrual cycle irregularities and hormone imbalances affect conception and fertility.

All of your reproductive and thyroid hormones need to be in the right delicate balance for conception to work. Fortunately, studies show that when hypothyroid women are treated, prolactin goes down and conception rates go up.

What next?

So now you understand how important it is to optimize your thyroid levels in order to have a healthy and fertile cycle.

Check out this post, which is all about treating hypothyroidism, and this post about testing for it.

Please ask any questions below, and reach out if want help with your thyroid!