Thyroid Problems in Pregnancy: Signs, Tests, Care

Thyroid problems are among the most common medical conditions in pregnancy, and with treatment most women have a healthy baby. The thyroid is a small gland in the neck that makes hormones controlling energy, heart rate and metabolism. In pregnancy it also supports your baby's brain and nervous system.

An underactive thyroid (hypothyroidism) is more common than an overactive one (hyperthyroidism). Both are found with a simple blood test and managed with regular monitoring, as explained below.

Why the Thyroid Matters in Pregnancy

NIDDK explains that in the first trimester the baby depends on thyroid hormone from the mother, which crosses the placenta. The baby's own thyroid does not make enough hormone until about 18 to 20 weeks. That is why a thyroid condition in the mother, if left untreated, can matter early on.

Pregnancy itself changes thyroid hormone levels, and the body needs more iodine. A review in Thyroid Research notes that subclinical hypothyroidism, a mild form, may affect around 10 to 15 percent of women around pregnancy, or possibly more. Most cases are autoimmune.

Hypothyroidism: Underactive Thyroid

This happens when the gland makes too little hormone. It is usually caused by an autoimmune condition called Hashimoto's disease. Symptoms may include:

• Extreme tiredness
• Feeling cold more than others
• Muscle cramps
• Severe constipation
• Poor memory or concentration

Most cases are mild, and many symptoms overlap with normal pregnancy, so blood tests are the only way to be sure. If untreated, NIDDK lists risks such as preeclampsia, anaemia, miscarriage, low birth weight and, especially when untreated in the first trimester, developmental problems for the baby. A 2022 clinical guideline from Brazil gives similar risks.

Hyperthyroidism: Overactive Thyroid

Here the gland makes too much hormone, most often because of Graves' disease. Signs include a fast or irregular heartbeat, shaky hands, heat intolerance and weight loss or poor weight gain. Some of these are also normal in pregnancy. Untreated, it can raise the risk of miscarriage, premature birth, low birth weight and preeclampsia. Our guide to preeclampsia warning signs explains that condition.

Mild hyperthyroidism often needs no treatment. When medicine is needed, your doctor may prescribe antithyroid tablets and will choose the type for each stage of pregnancy. Radioactive iodine is not used in pregnancy.

When to be cautious: if you take thyroid medicine and become pregnant, do not stop it or change it yourself. Tell your doctor straight away, because the dose often needs to be adjusted.

Who Should Be Tested?

Guidelines vary on this. A Brazilian guideline recommends testing TSH for every woman early in pregnancy, or before it, where resources allow, noting that almost half of thyroid problems were missed when only high-risk women were tested. Where resources are limited, it suggests testing higher-risk women, such as those with:

• A past or current thyroid problem, goitre or thyroid surgery
• Type 1 diabetes or another autoimmune condition

Ask your doctor whether you fall into a higher-risk group. Testing is a blood test that measures TSH, and sometimes thyroid hormone and antibodies. Normal ranges change with the stage of pregnancy, so your doctor must interpret your result, not an internet chart.

Treatment and Monitoring

• Underactive thyroid: your doctor may prescribe thyroid hormone replacement tablets. If you already take them, you often need a higher dose in pregnancy.
• Overactive thyroid: mild cases are watched, and more severe cases are treated with medicine. Surgery is sometimes used when medicine cannot be taken.
• Blood tests: NIDDK says women with hypothyroidism are generally tested every 4 to 6 weeks in the first half of pregnancy and at least once after 30 weeks.
• Antibody tests: these can find the autoimmune cause and show who is more likely to have thyroid problems after birth.

Tip: take your thyroid tablet at the same time each day, and ask your doctor how far apart to take it from iron or calcium tablets, because these can interfere with absorption. See also folic acid and prenatal vitamins.

Iodine and Diet

Iodine helps the thyroid work, and needs rise in pregnancy and breastfeeding. NIDDK lists dairy, seafood, eggs, meat, poultry and iodised salt as sources. Too much iodine, for example from seaweed supplements, can also cause thyroid problems, so ask your doctor before taking any iodine supplement.

After the Baby Arrives

About 1 in 20 women develop postpartum thyroiditis, an inflammation of the thyroid, in the first year after birth, according to NIDDK. Its symptoms can look like baby blues or tiredness after birth, so ask for a thyroid test if tiredness, mood changes or palpitations persist. Our article on postpartum depression and support covers when to seek help for low mood.

Questions to Ask Your Doctor

1. Should I have a thyroid blood test now, and how often should it be repeated?
2. If I take thyroid tablets, do I need a change in dose now that I am pregnant?
3. When should I take my tablet in relation to meals and my other supplements?
4. Which symptoms mean I should call you or come in sooner?
5. Will I need extra scans or specialist review?
6. Should my thyroid be checked again after delivery?

Write the answers in your antenatal file so that every doctor who sees you knows your thyroid history.

When to See a Doctor

Talk to a doctor if you have a known thyroid condition and are planning pregnancy, or if you notice a fast heartbeat, tremor, extreme tiredness, weight changes or a swelling in the neck. Women with thyroid disease may need high-risk pregnancy care if the condition is not well controlled. Planning ahead with a preconception checkup helps.

Talk to a Doctor

Chaitanya Hospital in Kadapa offers antenatal check-ups, where you can raise thyroid concerns. Book an appointment or call +91 944 103 0587. This article is for general awareness and is not a substitute for a doctor's advice.