Pregnancy Risk Factors: Thyroid Disease

Learn the risks of thyroid disease while pregnant

On the front part of the neck lies an important butterfly-shaped gland called the thyroid. This gland is responsible for the production of thyroid hormones (triiodothyronine (T3) and thyroxine (T4)). These hormones control how the body uses energy. In addition, the hormones regulate your metabolism, body weight, temperature, nervous system, muscle strength and heart rate.

Dysfunction of the thyroid glands leads to too much or too little production of hormones, causing thyroid disease. Hyperthyroidism, or overactive thyroid, is excess production of T3 and T4. On the other hand, hypothyroidism refers to low levels of thyroid hormones. The 2 conditions affect thyroid-stimulating hormone (TSH), which informs the thyroid to make T3 and T4.

It’s especially important for women with thyroid disease to consult their physician, obstetrician or maternity team before, during and after pregnancy. Management of the condition requires close observation and collaboration between obstetricians, endocrinologists and neonatologists.

Thyroid and pregnancy

Thyroid hormones help to develop the nervous system and brain system of the fetus. It’s important to maintain your levels of TSH between 0.2-2.5 mU/L during the first 3 months of pregnancy and 0.3-3 mU/L in the other trimesters. The baby depends on you entirely for the supply of hormones in the first trimester before starting to produce its own.

Iodine is an important component in producing thyroid hormones. Acute deficiency leads to pre-term delivery, miscarriages, stillbirths, congenital disorders, retarded growth, learning difficulties, speech and hearing issues in babies.

Pregnancy hyperthyroidism

Hyperthyroidism in pregnancy can lead to certain side effects on an unborn baby, including prematurity, low birth weight, intrauterine growth restrictions, neurobehavioral disorders, stillbirth or miscarriages. Severe hyperthyroidism, or thyroid storm, can have devastating consequences on the mother.

The most common form of hyperthyroidism in pregnancy is Graves' disease. The disorder causes the body to create antibodies called thyroid-stimulating immunoglobulin (TSI). TSI causes the thyroid to enlarge, overreact and produce excess thyroid hormones.

Though a faster heart rate, sensitivity to high temperatures, and tiredness are common indicators for pregnancy, they may also signify hyperthyroidism. Other signs and symptoms include:

  • Severe vomiting and nausea

  • Shaky hands

  • Low weight, despite normal or heightened appetite

  • Insomnia
  • Nervousness

  • Irregular heartbeats

  • Increased perspiration

  • Feeling irritable and anxious


Other possible symptoms include diarrhea, high fever, pre-eclampsia, rapid heart rates, dehydration, shock and congestive heart failure.

Hypothyroidism while pregnant

Hypothyroidism is due to Hashimoto thyroiditis. This is an autoimmune disorder that produces antibodies that attack the thyroid. The consequences lead to a damaged or inflamed thyroid, thereby creating fewer hormones. Babies who survive the pregnancy will likely have neurological development problems.

The effects on the baby from hypothyroidism include low birth weight, stillbirth, premature birth and miscarriage. While excessive fatigue and weight gain are normal in pregnancy, these signs are also associated with hypothyroidism. Others include:

  • Memory loss or problems with concentration

  • Anemia

  • Pre-eclampsia

  • Cramps and muscle aches
  • Constipation

  • Trouble coping with colds

  • Congestive heart failure

Diagnosing and treating thyroid conditions while pregnant

Healthcare providers determine thyroid levels in pregnancy through blood tests for TSH, T3 and T4 levels. Low levels of TSH and high amounts of T4 show hyperthyroidism. An iodine uptake test to measure the absorption of iodine by the thyroid can also indicate hyperthyroidism.

Blood tests showing high levels of TSH and low levels of T4 signify the presence of hypothyroidism. Abnormal levels of thyroid peroxidase (TPO) antibodies detect Hashimoto thyroiditis.

Pregnant and nursing moms should avoid the iodine test so as not to interfere with the baby's development. It’s recommended you wait for at least 1 year to try getting pregnant after a radioactive iodine test.

Doctors may use radioactive iodine treatment before pregnancy to destroy thyroid cells. Medical surgery to remove the overactive thyroid helps to maintain normal levels of T3 and T4. However, it’s essential to check your TSI levels during pregnancy, even if you have had surgery. Sometimes the TSI goes into the baby's bloodstream, causing them to produce excess hormones.

If you are expecting multiple births, it’s normal to experience temporal hyperthyroidism, known as transient gestational thyrotoxicosis. It’s caused by high levels of human chorionic gonadotropin (hCG). In this scenario, you don’t require medication as the condition normalizes after 14 to 18 weeks of pregnancy.

During pregnancy, antithyroid prescriptions help to manage the disease. Propylthiouracil (PTU), carbimazole (CM) and methimazole (MMI) are the common drugs for treating the condition. PTU is effective during the first trimester since MMI can cause defects in the baby when taken early.

Consult your physician to switch medications appropriately based on hormone fluctuations and avoid congenital disabilities or liver failure. Although surgery is rare during pregnancy, it’s best done during 4-6 months of pregnancy if necessary.

Antithyroid medication is strong and may have mild to severe symptoms. However, should you experience these signs when taking the drugs, stop and contact your doctor immediately:

  • Sharp pain in the abdomen

  • Unending sore throat
  • Fever

  • Yellow skin or whites in the eyes (jaundice)


Levothyroxine assists in the treatment of hypothyroidism. The drug acts similarly to T4 and is particularly helpful during the first trimester.

Consult with your doctor to know what amounts of levothyroxine you require if you have a history of hypothyroidism. You will need to increase dosage during pregnancy and reduce the amounts after birth. Your physician will guide you on the treatment plan for hypothyroidism.

Your pregnancy journey does not need to be stressful due to a pre-existing thyroid condition. At All About Women, we have expert physicians to help you with thyroid issues and your pregnancy. Make your appointment today for all your reproductive health needs.