Hypothyroidism and Fertility

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The thyroid is a gland that sits in your lower throat and secretes a hormone called thyroid hormone. Hypothyroidism is a condition that results when the gland does not produce enough of this hormone. The gland can also produce too much hormone, and this is called hyperthyroidism.

What can happen if you have hypothyroidism?

You can think of the action of thyroid hormone as revving up your body and keeping it functioning at the proper rate. Too little and things slow down, and too much causes things to go too fast. Common symptoms of hypothyroidism include fatigue, weight gain, constipation, loss of sex drive, hair loss, dry skin, loss of periods, and miscarriages.

What causes you to get hypothyroidism?

Most commonly hypothyroidism is a result of an autoimmune process (your immune system attacks your thyroid gland with antibodies) called Hashimoto’s thyroiditis. Other causes include surgery or radiation treatments.

How do we test for hypothyroidism?

The most sensitive way to track thyroid activity is indirectly, by measuring Thyroid Stimulating Hormone (TSH), a hormone that stimulates your thyroid to produce thyroid hormone. When thyroid function is low, the brain detects this and raises the TSH to stimulate the thyroid. A higher than normal TSH suggests that your body is detecting hypothyroidism.

What is a normal TSH level?

Traditionally, TSH levels from 0.5 to 5.0 were considered normal. Above 5, we would diagnose and treat for hypothyroidism. (If the patient doesn’t actually have any symptoms, we call it “subclinical hypothyroidism”).
More recently, some researchers suggest we should treat subclinical hypothyroidism when TSH is over 2.5. There is some controversy around this. When the TSH is elevated your doctor will often ask for additional tests to look for the antibodies that would indicate that this is the autoimmune form of hypothyroidism.

How can hypothyroidism affect fertility?

For starters, hypothyroidism can lead to irregular cycles. It also affects babies because they rely on their mother’s thyroid hormone levels for the first trimester because its thyroid is not fully functional until around 20 weeks of gestation. If you are hypothyroid early in the pregnancy, your baby is as well. This is clearly a problem when you have untreated overt hypothyroidism but it is debated how much of a problem is posed by subclinical hypothyroidism. Most physicians will err on the side of treatment for subclinical hypothyroidism when you are trying to become pregnant.

How is it treated?

Hypothyroidism is treated with a synthetic form of thyroid hormone called Levothyroxine. It can take some time to make sure the dose is correct and so often a repeat blood test will be done in 4-6 weeks. It takes about that long for the TSH to adjust to the Levothyroxine or for any change in the dose of this medication. Monitoring is important to make sure you are getting enough thyroid hormone and also to make sure you are not getting too much.
Levothyroxine is a synthetic hormone with few impurities, very few side effects and produces almost no allergic reactions.

Once a patient is pregnant we will often increase dosing as pregnancy hormone interacts with TSH. We check TSH levels for all of our pregnant patients. If you are taking Levothyroxine there is no harm in reminding us that you too may need to have your dose increased.

What is “natural” thyroid hormone and should you take it?

The main hormone secreted by your thyroid gland is T4 hormone. Your body will then convert this to T3 hormone, which is the more active form of thyroid hormone. Natural thyroid hormone is desiccated thyroid gland and contains T3 and T4. It may be dangerous as the levels are difficult to predict. Most endocrinologists prefer to give synthetic T4 and let your body decide how much to convert to T3.

More questions?
Ask us here! We want to help.

You can also visit www.thyroid.ca.

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