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Thyroid Function and Your Fertility

By Leigh Ann Woodruff, February 6, 2012

If you are experiencing menstrual irregularities and trying to get pregnant, it is a good idea to have your thyroid tested. An underactive or overactive thyroid could be at the root of your fertility issues.

It is somewhat difficult to determine whether the thyroid is exclusively the cause of infertility, because infertility is often caused by a combination of factors, according to Susan L. Treiser, M.D., a reproductive endocrinologist with IVF New Jersey, part of the Attain Fertility Center Network. "But I would say probably as frequently as 20 percent of the time, you'll see some sort of abnormality with thyroid function in patients who are trying to conceive," she says.

What Is the Thyroid?

The thyroid is a small gland found at the base of the neck that produces two main hormones: T4 (thyroxine) and a small amount of T3 (triiodothyonine). These hormones control such things as how fast you burn calories and how fast your heart beats. T3 thyroid may also regulate serotonin and norepinephrine levels in the brain.

T3 and T4 are regulated by another hormone — thyroid stimulating hormone (TSH). When the brain perceives a lowered T3 or T4 level, more TSH is produced to stimulate the thyroid to produce more of these hormones.

"There is a very complex relationship between the reproductive system and the endocrine system," Dr. Treiser explains. "And everything has to be in a perfect balance. So if there is an abnormality in the thyroid, it could lead to menstrual irregularities. It can lead to a loss of ovulation, or it could lead to a shortened second half of your menstrual cycle called a luteal phase defect, which can increase your chances of miscarriages."

A woman with thyroid issues could have the more common hypothyroid (underactive thyroid) or hyperthyroid (overactive thyroid).

Underactvie Thyroid: Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland is not producing enough of the T3 or T4 hormones. The TSH level is high. Symptoms include: trouble losing weight, easy weight gain, feeling sluggish and depressed, constipation, aching joints and muscles, and feeling cold.

Hypothyroidism can be difficult to diagnose because women may have no symptoms at all.

"Hypothyroidism is more common," Dr. Treiser says. "Even if you're not gaining weight, and not feeling tired and cold and lethargic, you could still have an abnormality with your thyroid."

Hypothyroidism is usually treated with thyroid replacement therapy in the form of oral synthetic T4 supplements. A common one is called Synthroid.

Overactive Thyroid: Hyperthyroidism

With hyperthyroidism, the thyroid gland is producing too much hormone, which makes your metabolism speed up. With hyperthyroidism, the TSH level is low. Symptoms include: weight loss, trouble maintaining weight. trouble sleeping, mood swings, feeling nervous and irritable, rapid and irregular heartbeat, and feeling hot.

"Some of the common things you see with hyperthyroidism are that all of the sudden, your heart starts to race, you feel an excessive heat a lot of the time," Dr. Treiser says. "Some people will notice a change in their eyes, which is when you get severe hyperthyroidism — something called Graves Disease."

Hyperthyroidism may be treated with antithyroid medication (for mild cases) or radioactive iodine, which destroys part of your thyroid gland. Sometimes treatment for hyperthyroidism can actually cause hypothyroidism.

Getting Your Thyroid Checked

Even if you don't have symptoms of hypothyroidism or hyperthyroidism, it is a good idea to have a simple, inexpensive thyroid test each year. The test determines whether too much or not enough TSH is being produced.

The normal range for TSH is O.4-4.5 mIU/L. New studies, however, have suggested that the level should be kept around 2 mIU/L during pregnancy. "You need to be monitored throughout the entire pregnancy because your thyroid requirements will change," Dr. Treiser explains. "And it's important to keep it closely controlled. Within the last few years, they are actually saying to keep it within the low end of normal during pregnancy. The importance of that in treating infertile women is to make sure that while they're trying to get pregnant— even before they get pregnant — you want to make sure that if they have evidence of hypothyroidism that you want to keep the TSH to around 2."

Whether hyper- or hypothyroid, under the care of a fertility specialist, women have very good chances of becoming pregnant. “There are risks and being monitored by a specialist throughout the pregnancy is extremely important,” says Dr. Treiser. “Women who are hyperthyroid may run the risk of having a low birth-weight baby or have problems with pre-term labor. Those with a hypothyroid may have a higher risk of miscarrying. The bottom line is that women with any type of thyroid issue need to work with a fertility specialist and be monitored regularly to ensure a healthy pregnancy.”

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