Revised 2018

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 successful pregnancy and 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 for pregnant women are different from those in the general non-pregnant population. This should be taken into account in interpreting thyroid function in pregnancy


  • Tell your midwife or doctor 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 should never be used during pregnancy
  • ‘Block and Replace’ regime of antithyroid drug therapy should not be 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 newborn 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 within six to twelve months after birth; it can clear up on its own but if hypothyroidism develops you may need a course of levothyroxine tablets

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.

This Quick Guide is one in a series about thyroid disorders. Other Quick Guides are available to read and download from the British Thyroid Foundation website. A leaflet containing more detailed information about Pregnancy and Fertility in Thyroid Disorders is also available.

The British Thyroid Foundation
tel: 01423 810093
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

Membership Information
Quick Guides

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, 2018
Our literature is reviewed every two years and revised if necessary.

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