Thyroid disease, if undiagnosed or uncontrolled, can make it harder to conceive and can cause problems during pregnancy. Monitoring and relevant dose changes are especially important in the first trimester (or first 12 weeks of pregnancy).
The following information is designed to help patients understand more about their thyroid disorder and how it may affect, or be affected by, pregnancy. If any of the information is not clear please discuss it with your GP, specialist or midwife and ask them to explain it to you.
If you are pregnant and have a history of thyroid disease (even if you are not on treatment now) for example
• subclinical hypothyroidism
• radioactive iodine treatment
• positive thyroid antibodies
speak to your GP and arrange thyroid blood tests as soon as you have a positive pregnancy test.
If you have an underactive thyroid (hypothyroidism)
• If you are planning a pregnancy you should speak to your GP to arrange thyroid blood tests and ideally aim for a Thyroid Stimulating Hormone (TSH) level of less than 2.5mU/l at the time of conception
• It is recommended that your TSH should be less than 2.5mU/l in the first trimester of pregnancy and less than 3.0mU/l after that
• As soon as you know you are pregnant it is usually recommended that your levothyroxine is increased immediately by 25-50mcg daily. You should then contact your GP and arrange to have a thyroid blood test
• If you have had thyroid cancer and are already on doses of levothyroxine that keeps your TSH level suppressed, you will probably not need to increase your levothyroxine but you should discuss this with your GP or specialist
• Thyroid blood tests should be checked every four to six weeks during pregnancy and with a further test a few weeks after delivery. It may not be necessary to test so frequently in later pregnancy if your thyroid levels are stable
• After delivery you will probably need to return to your pre-pregnancy dose of levothyroxine and patients taking levothyroxine for subclinical hypothyroidism may be able to stop treatment. You should discuss this with your GP or specialist before making any changes to your dose
• Breastfeeding is safe while taking levothyroxine
If you have an overactive thyroid (hyperthyroidism)
• Discuss your plans for pregnancy with your endocrinologist before you try to conceive as it may be necessary to change your medication, or in some cases it can be stopped
• Arrange to have thyroid blood tests checked as soon as pregnancy is confirmed
• If you are being treated with antithyroid drugs (e.g. carbimazole or Prophylthiouracil (PTU)) and you haven’t already discussed your pregnancy plans with them beforehand, you should contact your endocrinologist or GP as soon as possible after pregnancy is confirmed as it may be necessary to adjust your medication
• You may need to have your thyroid blood tests checked every four weeks throughout the pregnancy but not all patients will need checks this frequently. This will be decided by your endocrinologist
• If you are using antithyroid drugs and develop a rash, sore throat or an unexplained fever you must see a doctor immediately and ask for a full blood count to be arranged due to the small risk of agranulocytosis (low white blood cells)
• People using PTU have a very small risk of liver problems so if you notice any itching or yellowing of your eyes you must see a doctor immediately
• Breastfeeding while taking antithyroid drugs is generally safe but check with your endocrinologist
For further information or advice please speak to your GP or specialist doctor.
This information has been endorsed by the British Thyroid Association
For further information about thyroid and pregnancy see the following