Understanding thyroid problems during pregnancy

You’re pregnant—congratulations! 

You knew your body would go through nine months of major changes, but you weren’t prepared for this. You’ve been feeling crazy tired, super nauseous, and uncomfortably constipated. Your weight gain is also getting out of control. All normal? Maybe. But these can also be signs of a thyroid problem.

Your thyroid is a small, butterfly-shaped gland at the front of your neck, by the base of the throat. It’s part of the body’s endocrine system, a series of glands that influence nearly every cell and organ in your body. Your thyroid might be tiny, but the hormones it produces—thyroxine (T4) and triiodothyronine (T3)—are responsible for a lot of major bodily processes, such as regulating your metabolism (the way your body uses calories and energy), body temperature, and heart, digestive, and muscle functions. 

When your thyroid doesn’t produce enough thyroid hormones, you have what doctors call hypothyroidism, or an underactive thyroid. Hyperthyroidism, or having an overactive thyroid, occurs when your levels of thyroid hormones are too high. 

For reasons that aren’t fully understood, women are far more likely than men to have thyroid dysfunction. In fact, 80% of people with thyroid conditions are women—and pregnancy, with the cascade of hormones it produces, can be a tricky period for a woman’s thyroid. The American Thyroid Association reports that roughly 3% of pregnant women have hypothyroidism in pregnancy. Hyperthyroidism affects fewer than 1 in 100 pregnant women, says Stanford Children’s Health.

RELATED: Pregnancy statistics 2024

What’s the connection between the thyroid and pregnancy?

Your fetus needs a healthy supply of thyroid hormones to properly grow—especially in the first trimester of pregnancy, during nervous system and brain development. With a normal, healthy pregnancy, your thyroid gland enlarges and, stimulated by an increase in circulating levels of the hormone HCg, makes more thyroid hormones—up to 50% more. 

That’s important, seeing as your baby can’t fully make enough thyroid hormones to support itself until about 18 to 20 weeks of pregnancy, notes the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). “But if you have thyroid dysfunction, there will not be an appropriate rise in thyroid hormones and symptoms can occur,” says Tina Nguyen, MD, assistant professor of maternal-fetal medicine at the David Geffen School of Medicine at UCLA.

Who’s at high risk?

Women are not universally screened for thyroid disease in pregnancy unless they have certain risk factors. These include:

• Having a family history of thyroid disorders
• Having an autoimmune disorder (for example, type 1 diabetes or rheumatoid arthritis)
• Taking anti-thyroid medication (for hyperthyroidism) or receiving radioactive iodine (a treatment for thyroid cancer)
• Having had thyroid surgery or radiation to the neck area

Talk to your healthcare provider if you meet any of these criteria.

Can thyroid problems affect a pregnancy?

Thyroid hormones—whether there’s too much or too little—can have a profound effect on a pregnancy.

Hyperthyroidism in pregnancy

Hyperthyroidism, while rare during pregnancy, can cause problems for both a mom and her baby. They include:

• Preeclampsia (a condition that causes very high blood pressure during pregnancy)
• Premature delivery
• Low birth weight
• Miscarriage

What causes hyperthyroidism during pregnancy?

The most common cause of hyperthyroidism during pregnancy is an autoimmune condition called Graves’ disease. The condition causes antibodies (blood proteins the immune system produces to fight a foreign substance, and, sometimes, for reasons that aren’t entirely clear,  even healthy tissue and organs) to attack the thyroid gland. As a result, the thyroid becomes overactive and steps up production of thyroid hormones. 

Symptoms of hyperthyroidism

Symptoms of hyperthyroidism include:

• Thin, brittle hair
• Irritability
• Feeling uncomfortably warm
• Bulging eyes
• Muscle weakness
• Fast heart rate
• Weight loss
• Goiter, which is an enlarged thyroid gland that appears as a bulge on the neck

Consult your healthcare provider if you’re experiencing any symptoms of hyperthyroidism. According to Stanford Children’s Health, severe, uncontrolled hyperthyroidism can be fatal for a mom-to-be. Women with hyperthyroidism during pregnancy can also experience postpartum thyroiditis, or an inflammation of the thyroid gland, after delivering.

Treatment for hyperthyroidism and pregnancy

The first-line drug to treat hyperthyroidism in pregnancy is propylthiouracil, according to the Endocrine Society. The common thyroid drug Tapazole (methimazole) can cause birth defects if taken too early during pregnancy.

Hypothyroidism and pregnancy

Doctors break hypothyroidism down into two categories: overt and subclinical. According to the American Thyroid Association, you’ll be classified as having overt hypothyroidism if your levels of T4 are low but another hormone, called thyroid-stimulating hormone (TSH), is high. Subclinical hypothyroidism is a milder case and occurs when your TSH levels are high but your T4 levels are normal.

Having too little thyroid hormone can cause a whole host of problems for women and their developing babies. For starters, according to research published in the Indian Journal of Endocrinology and Metabolism, if you’re a woman with untreated hypothyroidism, you’ll have more problems trying to conceive, as the disorder can cause irregular ovulation. Once you get pregnant, you’ll have higher rates of miscarriage and pregnancy complications like preeclampsia, anemia, and excessive bleeding after giving birth (postpartum hemmorhage). The March of Dimes reports that babies born to moms with untreated hypothyroidism are at higher risk of:

• Premature birth
• Stillbirth and death in the first week of life
• Problems with their physical and intellectual development

What causes hypothyroidism during pregnancy?

The most common cause of hypothyroidism during pregnancy is an autoimmune disease called Hashimoto’s thyroiditis. This is a condition in which the body mistakes the cells of the thyroid gland as foreign invaders, inflaming the thyroid gland and damaging its cells to the extent that it can’t make enough thyroid hormones. 

It’s not that pregnancy causes the condition—or really any thyroid disorder, notes Cheryl R. Rosenfeld, DO, a spokesperson for the American Association of Clinical Endocrinologists (AACE). It’s that it may first be discovered during pregnancy. “The immune system of most women tends to quiet down during pregnancy,” she explains, “so most cases of autoimmune thyroid disease are patients with preexisting disease that becomes more apparent during pregnancy and is subsequently diagnosed.”

Symptoms of hypothyroidism

Common symptoms of hypothyroidism mimic a lot of the ones of early pregnancy, which means you can easily miss them. They include:

• Extreme fatigue
• Feeling nauseous
• Constipation

Additional signs are:

• Hair loss
• Dry skin/brittle nails
• Muscle weakness/cramps
• Shortness of breath with physical activity
• Hoarse voice
• Swelling 
• Goiter

Don’t hesitate to bring any of these symptoms to your healthcare provider’s attention. “Other signs of hypothyroidism you should definitely not ignore are feeling cold all the time, gaining a large amount of weight, and/or a slowing of your heart rate,” says Dr. Nguyen.

Treatment for hypothyroidism and pregnancy

Your healthcare provider can test your thyroid hormone levels with a simple blood test. When hypothyroidism is caught and treated early, most women can go on to have healthy pregnancy outcomes. The treatment of choice is a drug called Synthroid (levothyroxine), which replaces the T4 your body should naturally make. (T3 isn’t used in fetal brain development, so you don’t need to take it during pregnancy.) 

“[Levothyroxine] is even more crucial to take during pregnancy,” says Omayra Qujano-Vega, MD, an endocrinologist with Paloma Health, an online medical practice devoted solely to hypothyroidism. Dr. Qujano-Vega says it’s the only medication for hypothyroidism rated by the FDA as a pregnancy category A, meaning there are no risks to the fetus. “Even [most] prenatal vitamins have a pregnancy category of B, though they are highly safe and recommended.”

RELATED: Hypothyroidism treatments and medications

Wondering about natural remedies? “There are none considered safe and effective for use during pregnancy,” Dr. Rosenfeld says.For the best prices on levothyroxine treatment and thousands of other drugs, use your SingleCare discount card.