thyroid in pregnancy

Overview

The thyroid is a small, butterfly-shaped gland in your neck that makes hormones which control your energy, heart rate, and growth. During pregnancy, the thyroid can become underactive (not making enough thyroid hormone) or overactive (making too much). Both can affect you and your baby, but with regular monitoring and treatment, most women have healthy pregnancies and healthy babies.

Thyroid problems in pregnancy are fairly common. Around 2 to 3 in every 100 pregnant women have some form of thyroid condition, most often an underactive thyroid.

It can affect any pregnant woman. You are more likely to have thyroid problems if you have a family history of thyroid disease, a personal history of an autoimmune condition such as type 1 diabetes, or a thyroid condition that was diagnosed before pregnancy.

Symptoms

Common symptoms

• Feeling very tired or weak
• Unexpected weight gain or weight loss during pregnancy
• Feeling too cold or too hot when others feel fine
• A fast or pounding heartbeat
• Constipation or looser stools
• Mood changes, anxiety, or low mood

Symptoms in children

• Thyroid problems mainly affect the baby while they are growing in the womb, but the baby may not show obvious symptoms before birth.
• After birth, babies are checked for thyroid problems through routine newborn screening. Signs of a thyroid issue in a baby can include poor feeding, slow growth, low muscle tone, and excessive sleepiness.

Symptoms in older adults

• For women over 35, thyroid symptoms can be easy to confuse with pregnancy tiredness or normal ageing.
• In older mothers, a fast heartbeat, high blood pressure, and feeling very anxious can be more noticeable and should be checked.

Causes

Main causes

• Pregnancy hormones, especially hCG and oestrogen, change how the thyroid works and can put extra strain on it.
• The immune system can sometimes attack the thyroid gland, causing an autoimmune thyroid condition.
• A lack of iodine — a mineral the thyroid needs to make hormones — can cause thyroid problems.
• A pre-existing thyroid condition may change during pregnancy, either getting better or worse.

Risk factors

• Family history of thyroid disease or autoimmune disease
• A personal history of an autoimmune condition, such as type 1 diabetes or lupus
• Previous thyroid surgery or previous treatment for thyroid disease
• Living in an area with low iodine in the diet
• Being older during pregnancy, although it can happen at any age

When to see a doctor

See a doctor urgently if:

• If you have any of the emergency symptoms listed above
• If you feel your heart racing while you are resting
• If you are vomiting so much that you cannot keep fluids down
• If you have high blood pressure readings or a severe headache with vision changes

Book a routine appointment if:

• If you are pregnant and already have a thyroid condition, book an early review with your doctor or specialist
• If you have ongoing tiredness, weight changes, mood changes, or palpitations, mention them at your antenatal appointment
• If you are planning pregnancy and have a thyroid condition, ask for a thyroid check before you conceive
• If you notice swelling in your neck or a feeling of pressure when swallowing

Diagnosis

Your doctor or midwife will ask about your symptoms, medical history, and family history. They may also feel your neck to check for swelling. A small blood sample is then taken to measure your thyroid hormone levels.

Tests that may be done

• Blood test for TSH (thyroid-stimulating hormone) — this is the main hormone that controls your thyroid
• Blood test for thyroid hormones called free T4 and free T3
• Blood test for thyroid antibodies, if an autoimmune cause is suspected
• An ultrasound scan of your thyroid in some cases

What to expect at your appointment

The blood test is quick and needs no special preparation. You usually get results within a few days. If the results are not normal, you may be referred to an endocrinologist (a hormone specialist) and an obstetrician so that your pregnancy and thyroid are monitored together.

Treatment

The goal is to keep your thyroid hormone levels in a healthy pregnancy range. Treatment depends on whether your thyroid is underactive or overactive. You may need no treatment and just monitoring, or you may need medication that is adjusted carefully throughout pregnancy. After birth, your treatment is usually changed again.

Self-care at home

• Take any prescribed medication exactly as your doctor advises, even if you feel well
• Do not stop or change your thyroid medication on your own — doses often need to change during pregnancy
• Attend every antenatal and thyroid check-up
• Do not take iodine supplements unless your doctor or midwife specifically recommends them
• Tell every health professional you see that you are pregnant

Medical treatments

For an underactive thyroid, doctors usually prescribe thyroid hormone replacement medication — a pill that replaces the hormone your body is missing. For an overactive thyroid, treatment may include medication that reduces thyroid activity. The type of medicine and dose are chosen carefully for pregnancy, and blood tests are done regularly to keep the dose right. Radioactive iodine treatment is never used during pregnancy.

When is surgery considered?

Surgery to remove part or all of the thyroid is very rarely needed during pregnancy. It may be considered if medication is not controlling an overactive thyroid, or if there is a suspicious thyroid nodule. If surgery is needed, it is usually planned for the second trimester.

Living with this condition

Living with a thyroid condition in pregnancy means having a few extra appointments and blood tests, but for most women it is very manageable. Keep your results in a folder, take your medication as directed, and tell your maternity team about any new symptoms. You will be monitored closely through pregnancy and for a few weeks after birth.

Lifestyle tips

• Get enough rest and sleep, but try to stay gently active
• Learn simple ways to manage stress, such as slow breathing or short walks
• Avoid smoking and alcohol
• Take only the vitamins or supplements recommended by your maternity team

Diet and exercise

Most women with thyroid problems do not need a special diet, but you do need enough iodine — found in milk, yogurt, fish, and eggs — along with a balanced pregnancy diet. If you have food restrictions, ask to speak to a dietitian. Gentle exercise such as walking or pregnancy yoga is usually safe, but check with your midwife before starting.

Mental health and emotional wellbeing

Thyroid problems can make you feel low, anxious, or more emotional, and pregnancy can make these feelings stronger. These feelings are not your fault. Talk to your midwife or doctor honestly — they can help and arrange the right support. You deserve help, not judgement.

Prevention

Not all thyroid problems can be prevented, because many are caused by immune system changes or by normal pregnancy hormones. The best step is to have your thyroid checked before pregnancy if you already have a thyroid condition, and to attend routine antenatal care. If you live in an area with low iodine, eating iodine-rich foods can help, but do not take extra iodine supplements unless a doctor recommends them.

Vaccines

Vaccines do not prevent thyroid problems, but staying up to date with recommended vaccinations during pregnancy is important for your health and your baby's health.

Screening programmes

In many countries, thyroid blood tests are not done routinely for every pregnant woman. You can ask your midwife or doctor for a thyroid test if you have symptoms, a known thyroid condition, or risk factors like a family history of thyroid disease.

Complications

If left untreated

• An underactive thyroid that is not treated may increase the risk of miscarriage, preterm birth, or pre-eclampsia (high blood pressure in pregnancy)
• An overactive thyroid that is not controlled can lead to low birth weight, premature delivery, or problems with the baby's thyroid
• A sudden and severe flare-up called thyroid storm is an emergency and can be dangerous for both mother and baby
• Thyroid antibodies can rarely cross the placenta and affect the baby's own thyroid function

Long-term outlook

With early detection and careful monitoring, the great majority of women with thyroid problems in pregnancy have healthy pregnancies and healthy babies. After birth, your thyroid usually returns to how it was before pregnancy, though some women need ongoing treatment. Your care team will support you through every step, including after your baby arrives.

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