How Thyroid Disease Can Affect Your Fertility

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The thyroid gland is part of your endocrine system, along with your reproductive glands. When your thyroid is not healthy or fully functional, it can affect your ability to get pregnant. Let’s explore some of the ways thyroid disease can affect your fertility.


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Your ovulation can be affected

To get pregnant, your ovaries need to release an egg. When your thyroid function is not optimized, you are at risk of having cycles when you don’t release an egg, even though you still have a menstrual period. This is known as anovulation.

Are you ovulating? You can use an ovulation predictor test kit to measure hormones. Or, you may want to use the fertility awareness method to chart common ovulatory signs, such as body temperature and changes in cervical mucus.


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Your menstrual cycle can be erratic

Thyroid dysfunction can cause an irregular menstrual cycle, in particular, a luteal phase defect. Normally, the luteal phase — the time between ovulation and menstruation — is from 13-15 days, enough time for an egg to be fertilized, travel through your fallopian tube, and implant successfully. If that phase is too short, implantation can be interrupted and the fertilized egg expelled during menstruation.


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Is your luteal phase long enough?

Is your luteal phase long enough? You can find out by charting your fertility. The book “Taking Charge of Your Fertility” by Toni Wechsler has helpful charts to track your fertility and estimate your luteal phase. In some cases, your physician may test your follicle-stimulating hormone (FSH), luteinizing hormone (LH), and progesterone levels to help identify luteal phase defects.


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Your progesterone levels can be affected

Thyroid irregularities can trigger low progesterone. Progesterone is essential for healthy conception, development of a healthy lining of the uterus, and successful implantation.

Are you low on progesterone? Testing before pregnancy and after conception can establish your levels. If low, supplemental progesterone — prescription oral, injectable, suppository, and creams, as well as over-the-counter creams — can restore levels to normal for optimal fertility.


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You may experience early perimenopausal changes

The average age of menopause — defined as a year since your last menstrual period — is 51. Perimenopause — when you are still menstruating, but estrogen and progesterone levels fluctuate and anovulatory cycles become more common — typically starts as many as 10 years before menopause. Women with autoimmune Hashimoto’s disease, however, have a somewhat increased risk of an earlier perimenopause and menopause. This means that if you are in your mid to late 30s, and trying to conceive, thyroid irregularities may make that more difficult.


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Are you in early perimenopause?

Measurement of your ovarian reserve— the number of eggs you still have remaining — can help determine your fertility status. Also, tracking your cycles, measuring estrogen and progesterone levels, and measuring hormones such as FSH and LH that rise during perimenopause — can help determine your perimenopausal status. If you are showing signs of perimenopause, assisted reproduction techniques (ART) may be an option.


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Your estrogen levels may be unbalanced

Cells in your body have receptors for thyroid hormone. Estrogen also binds to those same receptors. If you have elevated estrogen levels — known as estrogen dominance — they can bind to your receptors and keep thyroid hormone from reaching your cells, which can impair your fertility.

Are you estrogen dominant? Your doctor can run blood or saliva tests to evaluate your estrogen levels. There are supplements and medications that can help modulate estrogen dominance and improve your fertility.


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You may have problems converting pregnenolone

Dietary cholesterol is converted into the hormone pregnenolone, by thyroid hormone. Pregnenolone becomes progesterone, estrogen, and other hormones. If your thyroid is dysfunctional, you can have low levels of key hormones needed for a normal menstrual cycle and successful conception.

Are you low in pregnenolone? Your doctor can run blood tests to evaluate your hormonal status. Hormone replacement therapy may help you successfully conceive.


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Your prolactin levels can be elevated

A malfunctioning thyroid can trigger high prolactin levels. Prolactin promotes milk production, and high levels while breastfeeding help prevent pregnancy in some women. Excess prolactin —hyperprolactinemia— can trigger irregular ovulation and anovulation.

Are your prolactin levels too high? A simple blood test can detect hyperprolactinemia. There are several prescription drugs, such as bromocriptine or cabergoline that can lower levels and help you have normal menstrual cycles and ovulation.


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Your sex hormone binding globulin (SHBG) can be too high

Lower levels of thyroid hormone can reduce your levels of a key hormone: sex hormone binding globulin (SHBG). SHBG attaches to estrogen, so if you don’t have enough SHBG, this can cause high estrogen levels and estrogen dominance.

Is your SHBG too high? SHBG can be measured by a blood test, to evaluate whether a deficiency or excess is affecting your fertility. Elevated SHBG can be addressed by integrative physicians with dietary changes and supplements.


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You may be undermedicated

During pregnancy, a normal thyroid gland enlarges after conception so that it can produce significantly more thyroid hormone. If your thyroid is unable to ramp up production, your fertility can be impaired. The latest guidelines recommend a TSH level less than 2.0 for optimal fertility and conception.

Are you undermedicated? Blood tests can determine if your treatment is optimal. If your TSH is too high, an increased dosage of thyroid medication can aid in fertility.


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You may be iodine deficient

Your body produces thyroid hormone from the iodine you ingest. In early pregnancy, a normal thyroid enlarges significantly so that it can produce as much as 50 percent more thyroid hormone. Most of it goes to the baby during the first trimester, until his or her thyroid is developed and starts producing its own thyroid hormone. If you are deficient in iodine, your fertility can be negatively affected.


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Are you deficient in iodine?

Blood or urinary testing can measure your iodine status. Also, experts say that all women who are planning to conceive should take a prenatal daily vitamin that includes at least 150 mcg of iodine. (Note: Many prescription or over-the-counter prenatal vitamins lack iodine, so read the label.)


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You may have other autoimmune conditions

If you have Hashimoto’s disease, you are at increased risk of other autoimmune conditions that can affect fertility. Autoimmune oophoritis and antiphospholipid syndrome can both impair your fertility.

Do you have antibodies that can affect fertility? A reproductive immunologist can run comprehensive autoimmune panels to diagnose these conditions. In some cases, treatments such as intravenous immunoglobulin (IVIG) can help improve your fertility and chance for a healthy pregnancy.


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Fertility treatment and assisted reproduction may be less effective

Thyroid patients undergoing fertility treatments may have less success. If you have a stimulated cycle for egg harvesting, studies show you need more added thyroid hormone, earlier, compared to conceiving naturally.

Your fertility doctor should run a comprehensive thyroid panel — including TSH, free T4, free T3 — before fertility treatments, and throughout the process, to ensure optimal levels. Don't assume your doctor will monitor your thyroid; you may have to request these tests.


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You may need a specialist

Unfortunately, most obstetricians are not knowledgeable about thyroid treatment. Similarly, many endocrinologists are not well-trained in managing fertility in their thyroid patients. Surprisingly, many fertility doctors and clinics overlook the impact of thyroid function on fertility and assisted reproduction.

As a result, in addition to an obstetrician, you may want to have a reproductive endocrinologist who specializes in hormonal issues as part of your medical care.