Can Thyroid Medication Reduce Your Risk of Pregnancy Complications?

Note: The Pregistry website includes expert reports on more than 2000 medications, 300 diseases, and 150 common exposures during pregnancy and lactation. For the topic Thyroid Disease, go here. For the topic Hyperthyroidism, go here. For the topic Hypothyroidism, go here. These expert reports are free of charge and can be saved and shared.


The thyroid is a small, butterfly-shaped gland that sits near the front of your neck. It has been nicknamed “the great regulator” because it produces hormones that play roles in metabolism, hair and nail growth, maintaining body temperature, mood, and weight gain and loss, as well as many other processes.

During the first trimester of pregnancy, thyroid hormones are especially critical for healthy brain and nervous system development in your fetus. After about 12 weeks, the fetus’s own thyroid will begin to produce its own hormones, but it doesn’t make enough to cover its entire need until about 18 to 20 weeks of pregnancy. A woman’s thyroid hormone needs increase during pregnancy to account for these fetal requirements.

If your thyroid produces too many or too few thyroid hormones (diseases known as hyperthyroidism and hypothyroidism, respectively), you will have many symptoms throughout a multitude of body systems. If you have either of these conditions before you get pregnant, expect to pay close attention to your thyroid and symptoms related to your disease during your pregnancy.

Occasionally, pregnancy will cause symptoms of high or low thyroid hormone levels. Usually, symptoms of high thyroid hormone levels during pregnancy are similar to traditional hyperthyroidism: heart palpitations or irregular heartbeat, nervousness or anxiety, tremor in your hands, trouble sleeping, weight loss or lower-than-expected weight gain, or persistent vomiting. Symptoms of hypothyroidism are similar to normal pregnancy symptoms: extreme tiredness, weight gain, constipation, difficulty concentrating, sensitivity to cold, and muscle cramps. If you experience any new or worsening symptoms of either of these thyroid diseases, call your doctor. If thyroid disease is untreated during pregnancy, you may experience preterm birth, severe increases in blood pressure, miscarriage, and low birth weight of your baby, among other problems.

The main causes of thyroid disorders during pregnancy are autoimmune conditions. Diagnosis is made on the basis of symptoms, physical exam, and blood tests to measure hormone levels. Luckily, treatment for both high and low thyroid hormone levels is fairly straight-forward and is generally safe during pregnancy. For hyperthyroidism during the first trimester, a medication (propylthiouracil [PTU]) is given to block the thyroid’s production of hormones; treatment in the second and third trimesters is usually accomplished with methimazole. If neither of these medications resolve the hyperthyroidism, surgery to remove the thyroid may be required.

Hypothyroidism is treated with a synthetic (man-made) hormone called levothyroxine, which is similar to the hormone made naturally by the thyroid. The dose will be monitored closely during pregnancy and adjusted, as needed, to maintain normal, healthy levels of thyroid hormones. If you were taking levothyroxine before pregnancy, your dose will likely need to be increased during pregnancy.

Changes in thyroid function can lead to poor outcomes for both mother and baby. Complications depend on the severity of the dysfunction and whether the hormone levels are too high or too low. Unfortunately, some of the symptoms of thyroid dysfunction are difficult to distinguish from normal pregnancy symptoms, so it is important to discuss all your symptoms and body changes with your doctor. If treatment for thyroid disorder is needed during pregnancy, early diagnosis and rapid intervention usually lead to the best outcomes. Maintaining healthy thyroid hormone levels decreases the risk of maternal and fetal complications and increases the chance of a healthy, full-term pregnancy.

Jennifer Gibson
Dr. Jennifer Gibson earned a Bachelor of Science degree in Biochemistry from Clemson University and a Doctor of Pharmacy degree from the Medical College of Virginia School of Pharmacy at Virginia Commonwealth University. She trained as a hospital pharmacist and is the author of clinical textbooks, peer-reviewed journal articles, and continuing education programs for the medical community, as well as a contributor to award-winning healthcare blogs and websites. In her free time, she enjoys running, reading, traveling, and spending time with her family.

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