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Thyroid dysfunction and pregnancy

Key facts

  • The thyroid is a gland inside your neck that produces thyroid hormone, which is vital to maintain your health and your baby's health during pregnancy.
  • Your thyroid may become underactive (hypothyroidism) or overactive (hyperthyroidism) during pregnancy.
  • Your doctor can detect unusual thyroid hormone levels with a blood test.
  • If you have problems with your thyroid, your doctor may prescribe medicines to help.
  • It's recommended to take an iodine supplement before and during pregnancy to keep your thyroid healthy.

    • What is the thyroid?

    The thyroid gland (Opens in new tab) is a gland inside your neck that produces hormones (Opens in new tab). These hormones control how your body makes and uses energy and are vital to maintain your health. They are also important in supporting your baby's health and development during pregnancy.

    The main thyroid hormone is called thyroxine or T4.

    Illustration showing the location of the thyroid gland in the neck.

    Illustration showing the location of the thyroid gland in the neck.

    What are some common thyroid problems?

    Thyroid problems happen when your thyroid doesn't work properly. There are several types of thyroid problems, including:

    • hypothyroidism (Opens in new tab) (underactive thyroid) — when your thyroid gland produces too little thyroid hormone, causing your bodily functions (metabolism) to slow down
    • hyperthyroidism (Opens in new tab) (overactive thyroid) — when your thyroid gland produces too much thyroid hormone, causing your bodily functions (metabolism) to speed up
    • thyroid nodules — abnormal growths or lumps in the thyroid gland, which can sometimes cause your body to make too much thyroid hormone
    • thyroid cancer (Opens in new tab)

    How does pregnancy affect thyroid function?

    Thyroid hormone levels increase during pregnancy to support you and your baby. While your baby's own thyroid starts working by week 12 of pregnancy, it doesn't produce enough hormone until 18 to 20 weeks. Until then, your baby relies on your supply of thyroid hormone for their brain development.

    Thyroid problems affect at least 1 in every 25 pregnancies. Your thyroid problem may have started before your pregnancy, or it may be first diagnosed during pregnancy.

    What are the symptoms of thyroid problems?

    The type of symptoms you have depend on if your thyroid gland is too active, or not active enough.

    Hypothyroidism

    Symptoms of an underactive thyroid include:

    Some people may not notice any symptoms.

    Hyperthyroidism

    Symptoms of an overactive thyroid include:

    CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

    What causes thyroid problems?

    Hypothyroidism

    An underactive thyroid can be due to:

    Hyperthyroidism

    An overactive thyroid can be due to:

    When should I see my doctor?

    If you are pregnant and have symptoms of thyroid problems, see your doctor and discuss your concerns.

    If you know you have a thyroid condition (Opens in new tab), it's a good idea to see your doctor to check your thyroid (Opens in new tab) while planning your pregnancy and again once you are pregnant. Your doctor will tell you how often you need a check-up.

    FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

    How are hypothyroidism and hyperthyroidism diagnosed?

    Your doctor can diagnose hypothyroidism and hyperthyroidism with a blood test (Opens in new tab).

    Your doctor will refer you for a blood test if you're pregnant and have:

    They might also refer you for a blood test to check your thyroid if you:

    How are thyroid problems in pregnancy treated?

    If you have a thyroid problem, you should have blood tests regularly throughout pregnancy to make sure your thyroid hormone level stays in the recommended range.

    If you have hypothyroidism, your doctor may prescribe a medicine called thyroxine (Opens in new tab). If you were already taking thyroxine before pregnancy, you may need to increase your dose when you become pregnant. Ask your doctor how much to take.

    If you have hyperthyroidism, your doctor or specialist may prescribe an anti-thyroid medicine, such as propylthiouracil (Opens in new tab) or carbimazole (Opens in new tab). If your thyroid is temporarily overactive because of pregnancy hormones, no treatment is usually needed.

    Can thyroid problems affect my baby?

    Hypothyroidism

    Low levels of thyroid hormone can cause complications such as:

    It may also affect your baby's brain development.

    If your hypothyroidism is treated effectively, it will not cause problems for you or your baby.

    Hyperthyroidism

    If your thyroid gland is overactive during pregnancy, it may cause complications such as:

    • miscarriage or stillbirth
    • low birth weight
    • preterm labour
    • pre-eclampsia

    Your baby may have a higher risk of developing hyperthyroidism. You and your baby may also have a higher risk of heart problems.

    Can thyroid problems in pregnancy be prevented?

    Not having enough iodine (Opens in new tab) in your body can cause low thyroid hormone levels. During pregnancy, your body needs more iodine than usual.

    Australian guidelines recommend that if you are pregnant, breastfeeding or planning to become pregnant, you should take a supplement containing 150 micrograms of iodine each day. This can be found in many pregnancy multivitamin supplements.

    Ask your pharmacist if any of your prescription or over-the-counter medicines could affect your iodine levels and thyroid function.

    Will my thyroid function return to normal after the baby is born?

    If you have hypothyroidism, you will usually be able to return to your pre-pregnancy thyroxine dose after the birth of your baby.

    After birth, about 1 in 25 people develop a thyroid problem called postpartum thyroiditis. This is when your thyroid becomes overactive for a short period, then becomes underactive, and finally returns to normal, within a year after the birth.

    Resources and support

    Read more about foods high in iodine (Opens in new tab).

    Visit the Australian Thyroid Foundation (Opens in new tab) for information and support.

    Aboriginal and/or Torres Strait Islander peoples

    Find an Aboriginal Community Controlled Health Organisation (ACCHO) (Opens in new tab) in your area.

    Speak to a maternal child health nurse

    Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 (Opens in new tab) or video call. Available 7am to midnight (AET), 7 days a week.

    Last reviewed: November 2024

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