Thyroid Problems in Pregnancy

Teresa was pregnant with her third baby. Unlike her previous pregnancies, which had been smooth and uneventful, she was experiencing more severe nausea and vomiting.

This was miserable.

What was going on? The first clue was revealed when she visited her midwife for her first prenatal visit. Her routine lab work showed a very low thyroid stimulating hormone (TSH). She was referred to my office for further evaluation. Here is what we talked about.

Understanding the thyroid

• The thyroid gland is a small butterfly-shaped organ which you can feel just below your Adam's apple. Its job is to make thyroid hormone, which controls your metabolic rate. This means your heart rate, your breathing rate, your temperature, and how quickly your cells produce energy.

• The thyroid gland is turned up and down by thyroid stimulating hormone (TSH). If your thyroid hormone level is low, more TSH is secreted from your brain to tell the thyroid gland to get busy. If there is an overproduction of thyroid hormone, then TSH will decrease, so that thyroid gland stimulation is reduced. Got that? Low thyroid hormone means higher TSH. When you have high thyroid hormone levels, you will usually have low TSH.

So what happens if your thyroid gland is making the wrong amount of thyroid hormone?

Hypothyroidism

Hypothyroidism happens when your thyroid gland is not making enough thyroid hormone.This can happen because of iodine deficiency. In the US, iodine deficiency is pretty uncommon because we have iodine added to our salt. The majority of hypothyroidism here is caused by Hashimoto's disease, an autoimmune condition where antibodies attack the thyroid gland and reduce the production of thyroid hormone.

Symptoms of hypothyroidism include:

• Fatigue

• Depression

• Constipation

• Feeling cold all the time

• Weight gain

• Lower heart rate

When you're pregnant, hypothyroidism may be harder to diagnose, because most pregnant women gain weight and are constipated. Another important fact about hypothyroidism in pregnancy is that it can affect your baby. Thyroid hormone is necessary for normal brain development in the baby. Pregnant moms who have untreated or undertreated hypothyroidism have a higher risk of having a baby with developmental delays. So if you have hypothyroidism, it's so important for you to take your medicine!

Hyperthyroidism

Hyperthyroidism is a condition where your thyroid gland makes too much thyroid hormone. Symptoms are:

• Nervousness

• Racing heart or palpitations

• Weight loss

• Feeling hot all the time

• High blood pressure

The most common cause of hyperthyroidism in pregnancy is Graves' disease, another autoimmune condition. With Graves disease, antibodies stimulate the thyroid to overproduce.In pregnancy, hyperthyroidism can lead to poor fetal growth and more nausea and vomiting. Remember our friend Teresa, with nausea and low TSH? When we completed a complete thyroid panel of labs, her thyroid hormone level was high - not a surprise. She also tested positive for thyroid-stimulating antibodies.

Medications for thyroid problems

The good news is thyroid problems are treatable. Here are some of the medications we use to treat thyroid disease:

• Levothyroxine - this is simply thyroid hormone. We use it to treat hypothyroidism. Usually, it's just a once daily dose.

• Methimazole and propylthiouracil (PTU) - these medications stop the thyroid gland from producing too much thyroid hormone.

• Beta-blockers - these are used to control a fast heart rate or high blood pressure if you have hyperthyroidism until your symptoms improve.

Diving deeper

There is a lot of information that we haven't talked about. Thyroid disease may also be caused by inflammation or thyroid nodules. Surgery or radiation are sometimes used to treat thyroid disease, but we don't use radiation in pregnancy because of risks to the fetus. If you have thyroid disease in pregnancy, your provider may check labs on you from time to time so that we can be sure your thyroid function is normal on medication.

We counseled Teresa that the thyroid-stimulating antibodies in Graves' disease may cross the placenta and also stimulate her fetus' thyroid gland. We placed her on medication; the medication also crosses the placenta and can counter the effects of the antibodies. We watched her fetus from month to month with ultrasound, to make sure he was growing normally and that his neck didn't look enlarged. And there was a happy ending: Teresa's nausea improved and her son was born healthy at full term.

In conclusion

If your provider tells you that your thyroid function is abnormal, don't sweat it (unless you are hyperthyroid, in which case you are probably already sweaty). (Sorry, a little medical humor.) Treatment is usually straightforward and safe, and outcomes tend to be good. Good luck!