Revised 2015

Undiagnosed thyroid disorders can cause fertility difficulties for both men and women, and problems during pregnancy. Once treated, normal fertility returns and you can expect to have a healthy baby.

What should I know?

It is very important to arrange to have a thyroid function test at your GP surgery if you have a thyroid disorder and are planning to conceive, or as soon as you know you are pregnant. Your doctor will take a blood test and then monitor your thyroid levels throughout your pregnancy. Thyroid hormone reference ranges in pregnant women differ from those quoted for the general population.and need to be interpreted carefully.


  • Tell your midwife or obstetrician about your thyroid disorder
  • If you are already taking levothyroxine it is recommended that the dosage is increased immediately by 25-50mcg daily once you know you are pregnant
  • Your doctor may further increase your levothyroxine dose during pregnancy
  • After your baby is born you should have a blood test. Your levothyroxine dose may be altered and usually returns to the dose that was recommended pre-pregnancy.


  • Tell your obstetrician about your thyroid disorder
  • Graves' disease is the most common cause of hyperthyroidism in pregnancy.
  • Some women, especially those with severe morning sickness, may develop a short term hyperthyroidism (gestational thyrotoxicosis) in the early weeks of pregnancy but this settles without the need for antithyroid drug therapy
  • If you are or have been treated for Graves’ disease, there is a very small chance that your baby will develop temporary hyperthyroidism, but this can be monitored and treated during pregnancy and for a short time after the birth if necessary
  • If you are taking antithyroid medication continue to take it during pregnancy
  • Propylthiouracil (PTU) is the treatment of choice when trying to conceive and during the first trimester (the first 12 weeks of pregnancy)
  • Radioactive iodine treatment is not used during pregnancy
  • ‘Block and Replace’ regime of antithyroid drug therapy is not used during pregnancy
  • Thyroid surgery is rarely required. If needed it should ideally be performed during the middle three months of pregnancy

After your baby is born

  • All new-born babies have a heel-prick blood test to check for hypothyroidism
  • You should arrange a blood test to check your thyroid hormone levels a few weeks after delivery
  • You can safely breast-feed whilst taking levothyroxine
  • Speak to your doctor if you wish to breast-feed whilst taking antithyroid medication
  • A disorder called postpartum thyroiditis - a temporary inflammation of the thyroid gland in the mother - may occur up to six months after birth; it can clear up on its own but if hypothyroidism develops you may need a course of levothyroxine tablets

It is well recognised that thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.

If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.

The British Thyroid Foundation
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

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Endorsed by:

The British Thyroid Association - medical professionals encouraging the highest standards in patient care and research

The British Association of Endocrine and Thyroid Surgeons - the representative body of British surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)

First issued: 2008
Revised: 2011, 2015
Our literature is reviewed every two years and revised if necessary.

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