Thyroid problems in pregnancy: underactive and overactive thyroid

Thyroid hormones matter for both a mother and her baby. If you have a thyroid condition and are pregnant, or planning to be, your doctor will want to watch it closely. This article explains what the NIDDK, NHS and MedlinePlus say. It is general education, not personal advice. Always follow your own doctor's guidance.

Underactive thyroid in pregnancy

The NIDDK says untreated hypothyroidism can affect both mother and baby. It says thyroid medicines can prevent these problems and are safe during pregnancy. Many women need higher doses, so it advises contacting your doctor right away on learning you are pregnant.

The NHS says that if you have an underactive thyroid and are pregnant or planning to be, you should tell your GP. You will need more tests, and your dose will likely need adjusting. It says that if left untreated, an underactive thyroid can increase the risk of pre-eclampsia, birth defects, premature birth and miscarriage, and that treatment usually helps prevent these problems.

Overactive thyroid in pregnancy

The NHS says poorly controlled or untreated overactive thyroid can be linked to pre-eclampsia, premature birth and miscarriage. The NIDDK says treatment options depend on factors including pregnancy:

• Radioiodine therapy is not used during pregnancy or breastfeeding.
• One antithyroid medicine is often used in early pregnancy, according to the NIDDK. Your doctor decides which medicine is suitable at each stage.
• Surgery may be considered for pregnant people who cannot take antithyroid medicine.
• For Graves' disease, a Doppler ultrasound is often used for diagnosis during pregnancy or breastfeeding instead of tests using radioiodine.

Iodine

The NIDDK says pregnant people need enough iodine because the baby relies on the mother's dietary intake, but too much iodine can cause a goitre in the baby. Doctors should advise on iodine needs during pregnancy. It also says people with Graves' or Hashimoto's disease may be sensitive to large amounts of iodine from seaweed such as kelp or dulse, supplements, some medicines or certain cough syrups. Do not take iodine or kelp supplements without asking your doctor.

After the birth

The NIDDK lists pregnancy within the past 6 months as a risk factor for both hypothyroidism and hyperthyroidism. MedlinePlus links to information on postpartum thyroiditis, which is a thyroid problem after birth. If you feel unusually tired, anxious, or notice neck swelling or a fast heartbeat after delivery, tell your doctor, because these have many possible causes.

Planning ahead

• Tell your GP or doctor about your thyroid condition before you try to conceive.
• Ask when your thyroid blood tests should be done during pregnancy.
• Ask how your medicine might change, but do not change it yourself.
• Mention any supplements, cough syrups or multivitamins you take.

Thyroid tests during pregnancy

MedlinePlus lists TSH, T4 and T3 as the standard blood tests for thyroid problems. The NIDDK says that for Graves' disease an ultrasound may be used rather than radioiodine tests during pregnancy. Your own team decides how often to test and which tests to use.

When to see a doctor

Contact your doctor or midwife as soon as you know you are pregnant if you have a thyroid condition, and sooner if you are planning pregnancy. Talk to them about symptoms such as a fast heartbeat, shakiness, extreme tiredness, feeling very cold, or swelling at the front of the neck.

Seek emergency help for chest pain, trouble breathing, a very fast or irregular heartbeat, fainting or confusion. In an emergency, call your local emergency number (112 in India, 911 in the United States).

This article is for education only and does not replace advice from your own doctor or midwife.