Your thyroid hormones and your reproductive (sex) hormones constantly interact. Throughout your life, this is always the case. Thyroid hormones affect when you start your period, then your cycle regularity and flow. They influence your ability to conceive a child, and then carry a pregnancy. Lastly, thyroid hormones even affect pre-menstrual and menopausal symptoms.
Your brain orchestrates thyroid AND sex hormones
You make thyroid stimulating hormone (TSH) in your brain, specifically in your pituitary gland. TSH signals your thyroid to make thyroid hormones.
Your pituitary gland makes other signaling hormones such as prolactin (PRL – grow breasts and make milk) and growth hormone (GH – grow babies). It also makes follicle stimulating hormone (FSH – develop follicles), and luteinizing hormone (LH – release an egg for ovulation). All of these signaling hormones, including TSH, are similar in structure, and influence each other.
These signaling hormones act in concert with TSH to stimulate follicle development and ovulation. This concert regulates your reproductive cycles.
Follicles house your eggs
Follicles are not the same thing as eggs. Instead, follicles are part of your ovarian lining. They house your oocytes (eggs). FSH signals healthier oocytes to mature, over the course of months, into antral follicles. During your follicular phase of your cycle, which is from the beginning of menstruation to ovulation, FSH typically signals one antral follicle to mature and ripen for ovulation.
Follicle growth depends on thyroid hormones
Your ovaries AND the oocytes in all your follicles have high numbers of TSH and 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. You may experience missed, heavy, or infrequent periods. Or you may experience shorter cycles, with more frequent periods. When they are heavy, you can lose a lot of blood!
Your thyroid hormones are essential for follicle development, ovulation, and a regular healthy period.
Low thyroid hormones can mess with your whole cycle
More than half of hypothyroid patients have menstrual irregularities. There are several scenarios that can happen to your menstrual cycle when you are hypothyroid. These are the most common:
1. Anovulation: no ovulation
Without the right amount of TSH and 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.
2. Luteal phase defect: too few days between ovulation and menstruation
After ovulation, the empty follicle sac that released your egg produces progesterone. Progesterone helps you have a sufficient luteal phase (between ovulation and menstruation). The ideal luteal phase length is 14 days.
With no ovulation, you won’t have enough progesterone. You might have a short luteal phase. It may come with PMS and spotting. You may have periods that happen close together.
3. Menorrhagia: heavy flow
Sometimes periods can be so heavy, the blood is “flooding.” Estrogen is the hormone that builds your uterine lining. Progesterone helps to thin your lining. With low progesterone, your uterine lining grows too much.
Hypothyroidism causes other sex hormone imbalances
I explained above how hypothyroidism in some 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.
Adolescent girls: delayed OR early puberty onset
Low thyroid hormones can cause a delayed onset of puberty. Or, girls may menstruate early because thyroid stimulating hormone is high, which acts on FSH and LH receptors, both of which ripen follicles. This means that follicles are stimulated to mature at a younger age because of high TSH.
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:
- If your follicles don’t mature properly, then you may not ovulate. With no egg, there’s no conception.
- High prolactin interferes with conception.
- If you don’t have enough progesterone, that will interfere with implantation success.
- 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.
After treatment for hypothyroidism, 76.6% of infertile women conceived within 6 weeks to 1 year. Infertile women with both hypothyroidism and hyperprolactinemia also responded to treatment and their PRL levels returned to normal.
Recommendations on conceiving with hypothyroidism
The American Thyroid Association (ATA) published task force findings on hypothyroidism and reproduction this year, 2017.
These are bullet point recommendations from these findings:
All women seeking care for infertility:
Evaluate serum TSH concentration.
Overt hypothyroidism (high TSH and low T4), natural conception:
LT4 treatment is recommended for infertile women with overt hypothyroidism who desire pregnancy.
Subclinical hypothyroidism (high TSH, normal T4), natural conception:
Insufficient data, so no recommendation for or against treatment. However, consider LT4 to prevent progression to more significant hypothyroidism once pregnancy is achieved. Furthermore, low dose LT4 therapy (25–50 μg/d) carries minimal risk.
Subclinical hypothyroidism, with IVF (in vitro fertilization) or ICSI (intracytoplasmic sperm injection):
Treat with LT4, to achieve a TSH concentration <2.5 mU/L.
Positive thyroid antibodies (TPO Ab), normal T4, natural conception:
No recommendation for LT4 therapy.
Positive thyroid antibodies, normal T4, ART (assisted reproductive technology like insemination and in vitro):
Insufficient evidence, however, consider LT4 given its potential benefits in comparison to its minimal risk. In such cases, 25–50 μg of LT4 is a typical starting dose. Glucocorticoid therapy is not recommended.
All women using ovarian stimulation medication (gonadotropins), during ART:
Perform thyroid function tests either before, or 1–2 weeks after, because results obtained during the course of controlled ovarian stimulation may be difficult to interpret. If TSH levels are high and pregnancy occurs, treat according to recommendations in the next post on Pregnancy and Hypothyroidism. If pregnancy is negative, retest TSH in 2-4 weeks to see if it has normalized.
Infertile women with PCOS and thyroid antibodies:
My recommendation: Thyroid antibodies exist in ovarian tissue and may interfere with follicle development, especially with the use of clomiphene citrate (“Clomid”). Many fertility specialists use a different medication, such as letrozole (Femara®).
For treatment of hypothyroidism to improve periods and fertility, see Conventional and Functional Medicine Approaches to Hypothyroid, and A Functional Medicine Approach to Hashimoto’s.
Read about Pregnancy and Hypothyroidism.
please ask questions or give feedback below!