Thyroid Conditions During Pregnancy: A Common and Manageable Challenge

The thyroid is a small gland in the neck that produces hormones regulating metabolism, energy, heart rate, body temperature, and a great many other functions that are easy to take for granted when it is working normally. During pregnancy, the thyroid is under additional demand — and for women who already have thyroid conditions, or who develop them during pregnancy, careful management is important for both maternal and fetal health.

Thyroid conditions in pregnancy are more common than many women realise. Hypothyroidism — an underactive thyroid — affects approximately two to three percent of pregnant women when diagnosed formally, and a significantly higher proportion have subclinical thyroid dysfunction that may not be diagnosed unless specifically screened for. India has a high burden of thyroid disease, partly due to iodine deficiency in certain populations and partly due to the high rates of autoimmune thyroid disease in South Asian women.

The reassuring reality is that thyroid conditions in pregnancy are well understood, there are effective treatments, and with appropriate monitoring and management, most women with thyroid disease have healthy pregnancies.

Why the thyroid is particularly important in pregnancy

During pregnancy, thyroid hormone production needs to increase by approximately forty to fifty percent. This is because the thyroid is responsible not only for the mother’s own metabolic needs — which increase during pregnancy — but also for supporting fetal brain and nervous system development, particularly in the first trimester before the fetal thyroid becomes functional.

The fetus depends entirely on maternal thyroid hormone for the first twelve weeks of pregnancy. Thyroid hormones are essential for normal brain development, neuronal migration, and early neurological organisation. Inadequate maternal thyroid hormone during this period is associated with impaired cognitive development and IQ in the child — which is why untreated hypothyroidism in early pregnancy carries fetal consequences that go beyond what most women are aware of.

After the first trimester, the fetal thyroid begins to function independently, but maternal thyroid hormone continues to contribute to fetal development throughout pregnancy.

Hypothyroidism in pregnancy

Hypothyroidism — too little thyroid hormone — is the most common thyroid condition in pregnancy. It may be:

Pre-existing hypothyroidism — diagnosed before pregnancy, typically managed with levothyroxine (thyroxine replacement). Pregnancy increases thyroid hormone requirements, so women who were stable on a fixed dose before pregnancy often need a dose increase in early pregnancy.

Newly diagnosed hypothyroidism — identified through screening or because symptoms prompted investigation during pregnancy.

Subclinical hypothyroidism — TSH (thyroid-stimulating hormone) is elevated but thyroid hormone levels (T4) are still within the normal range. The management of subclinical hypothyroidism in pregnancy is more nuanced and depends on the degree of TSH elevation, the presence of thyroid antibodies, and individual clinical factors.

Autoimmune hypothyroidism (Hashimoto’s thyroiditis) — the most common cause of hypothyroidism in women of reproductive age. The immune system produces antibodies that attack the thyroid gland, reducing its function. Women with Hashimoto’s are at higher risk of miscarriage and pregnancy complications, and the presence of thyroid antibodies even with normal thyroid function warrants monitoring.

Symptoms of hypothyroidism that may be noticed during pregnancy:

• Fatigue beyond what is expected for pregnancy
• Cold intolerance
• Weight gain beyond expected pregnancy weight
• Constipation (though this is common in pregnancy generally)
• Dry skin and hair
• Slowed heart rate
• Difficulty concentrating or memory problems

The challenge is that many of these symptoms overlap with normal pregnancy experiences, which is one reason thyroid conditions are often underdiagnosed without active screening.

Treatment — levothyroxine (synthetic thyroxine) is safe in pregnancy and is the standard treatment. The dose is adjusted based on TSH levels, which are monitored every four to six weeks in early pregnancy and every trimester once levels are stable. The target TSH in pregnancy is lower than outside pregnancy — your provider will advise the specific target appropriate for your situation and trimester.

Hyperthyroidism in pregnancy

Hyperthyroidism — too much thyroid hormone — is less common than hypothyroidism in pregnancy, but it is important to identify because untreated hyperthyroidism carries significant risks including preterm birth, fetal growth restriction, heart failure, and thyroid storm (a rare but life-threatening emergency).

Graves’ disease — an autoimmune condition in which antibodies stimulate the thyroid to overproduce hormone — is the most common cause of hyperthyroidism in pregnancy.

Gestational transient thyrotoxicosis — a condition specific to pregnancy in which high levels of hCG (the pregnancy hormone) stimulate the thyroid and cause temporary mild hyperthyroidism. It is usually associated with severe nausea and vomiting (hyperemesis gravidarum) and resolves on its own as hCG levels decline after the first trimester. It does not require antithyroid treatment.

Symptoms of hyperthyroidism in pregnancy:

• Rapid heartbeat or palpitations
• Tremors
• Excessive sweating
• Weight loss or failure to gain appropriate weight despite adequate appetite
• Heat intolerance
• Anxiety and restlessness

Treatment — antithyroid medications (propylthiouracil in the first trimester, carbimazole or methimazole in the second and third trimesters) are used to control hyperthyroidism. These medications cross the placenta and can affect fetal thyroid function, so dose management and fetal monitoring are part of care. The goal is to use the lowest effective dose to maintain thyroid hormone levels in a safe range without suppressing the fetal thyroid.

Thyroid screening in pregnancy

India does not have a universal pregnancy thyroid screening programme, though the Indian Thyroid Society and several obstetric guidelines recommend screening all pregnant women with TSH, particularly given the high rates of thyroid disease in the population.

In practice, screening varies between providers. Some providers routinely check thyroid function as part of first-trimester blood tests. Others screen selectively based on risk factors.

Risk factors that should prompt thyroid screening if you are not routinely offered it:

• Personal history of thyroid disease or previous thyroid surgery
• Family history of thyroid disease
• Presence of a goitre
• Type 1 diabetes or other autoimmune conditions
• Previous miscarriage or preterm birth
• Previous baby with thyroid problems
• Symptoms suggestive of thyroid dysfunction
• Infertility or subfertility that led to this pregnancy

If you have any of these risk factors and thyroid function has not been checked in this pregnancy, ask your provider about it.

What iodine has to do with thyroid health in pregnancy

The thyroid requires iodine to produce thyroid hormone. During pregnancy, iodine requirements increase significantly because of the higher thyroid hormone production needed and because some iodine is transferred to the fetus for fetal thyroid development.

Iodine deficiency — which remains a problem in some parts of India, particularly in mountainous regions away from seafood and iodised salt — can cause hypothyroidism in the mother and, in severe cases, cretinism (severe developmental delay) in the baby.

Iodised salt is the most reliable dietary source for most people. Dairy, eggs, and seafood also provide iodine. For women who don’t use iodised salt or who eat very restricted diets, iodine supplementation is worth discussing with a provider.

Note: excessive iodine can also harm thyroid function. Women with autoimmune thyroid disease should not take high-dose iodine supplements without medical guidance.

Postpartum thyroiditis

Postpartum thyroiditis is a thyroid condition that occurs after delivery, affecting approximately five to ten percent of women, with higher rates in women who had thyroid antibodies detected during pregnancy. It involves inflammation of the thyroid that can cause temporary hyperthyroidism (usually in the first few months after birth) followed by hypothyroidism (typically three to eight months postpartum), with eventual recovery to normal function in most women — though some develop permanent hypothyroidism.

Symptoms of postpartum thyroiditis can be attributed to the normal demands of new motherhood (fatigue, mood changes, difficulty losing weight), making it easy to miss. Women who had thyroid antibodies during pregnancy should have thyroid function checked at approximately three and six months postpartum.

The honest message

If you have a pre-existing thyroid condition and are pregnant, make sure your provider knows and that your thyroid function is being monitored more frequently than it was outside pregnancy. Dose adjustments are very commonly needed, and making them promptly matters for your baby’s early development.

If you have risk factors for thyroid disease and haven’t been screened, ask for TSH testing. It is a simple blood test and the information it provides is genuinely important.

Thyroid conditions in pregnancy are manageable. Levothyroxine, which is the primary treatment for the more common hypothyroid condition, is one of the safest medications used in pregnancy. The consequences of unmanaged thyroid dysfunction are significant; the consequences of well-managed thyroid disease are minimal. The difference between the two is screening, monitoring, and treatment — which this pregnancy is an opportunity to get right.

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This article is for general educational purposes only and does not replace personalised medical advice. Always consult your doctor, midwife, or an endocrinologist about thyroid function and management during pregnancy.