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Hypothyroid and Pregnant

Thyroid UK receives many request for help and support from women who are hypothyroid and pregnant and not sure what to do to preserve the health of their baby.

There has been a lot of research over the past few years in regard to pregnancy and thyroid disease which has led to more updated guidelines on this.  Hyperthyroidism and hypothyroidism can both result in problems with conception, increased risk of early miscarriage and adverse pregnancy and neonatal outcomes.​1​

Whether you are thinking about getting pregnant; are pregnant or are friends or family of someone who is pregnant, it’s important for you to know that untreated hypothyroidism, undertreated hypothyroidism and hyperthyroidism in pregnancy is bad for the baby.

The importance of the first 12 weeks

In the first trimester of pregnancy the foetus is dependent on maternal thyroid hormones for normal development of the brain; hence it is vitally important that adequate maternal levels of thyroid hormones are maintained.​2​

This means that during the first 12 weeks of pregnancy, the baby uses the mother’s thyroid hormone because its own thyroid gland does not become active until 12 weeks – although it doesn’t make enough thyroid hormone for its needs until around 18-20 weeks.2

So, if the mother has hypothyroidism and relies on levothyroxine or other thyroid hormone replacements, she may not have enough for herself and her baby.  If the baby does not get enough thyroxine from the mother this can cause a number of problems such as miscarriage and low IQ in infants.​2​

Research into whether women with subclinical hypothyroidism should be treated remains inconclusive.​3​

What to do if you are hypothyroid and pregnant

If you are hypothyroid and pregnant (or suspect you are), do speak to your doctor or endocrinologist about changes to your dose of levothyroxine or any other thyroid hormone replacement you are taking (such as liothyronine T3, or natural desiccated thyroid, and even thyroid glandulars).  Also, make sure you discuss with your doctor a referral to a thyroid specialist.

If you have subclinical hypothyroidism and are not yet on any treatment, do speak to your doctor before you try for a baby to check your levels. If you become pregnant, visit your doctor immediately to check your levels in case you become overtly hypothyroid and need treatment.

The British Thyroid Association Executive Committee state in their 2015 guidance, “Management of primary hypothyroidism” that, “The serum TSH reference range in pregnancy is 0.4–2.5 mU/l in the first trimester and 0.4–3.0 mU/l in the second and third trimesters or should be based on the trimester-specific reference range for the population if available.” ​4​

This is another very good reason for you to get your thyroid hormone levels checked if you are hypothyroid and pregnant.

Guidelines for when you are hypothyroid and pregnant


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  1. Jefferys A, Vanderpump M, Yasmin E. Thyroid dysfunction and reproductive health. Obstet Gynecol. Published online January 2015:39-45. doi:10.1111/tog.12161
  2. Barbour, M.D., M.S.P.H., FACP L. Thyroid disease and Pregnancy. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Published 2017.
  3. Maraka S, Singh O, Mastorakos G, O’Keeffe D. Subclinical Hypothyroidism in Women Planning Conception and During Pregnancy: Who Should Be Treated and How? J Endocr Soc. 2018;2(6):533-546. doi:10.1210/js.2018-00090
  4. Okosieme O, Gilbert J, Abraham P, et al. Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee. Clin Endocrinol. Published online June 25, 2015:799-808. doi:10.1111/cen.12824
  5. De Groot L, Abalovich M, Alexander EK, et al. Management of Thyroid Dysfunction during Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism. Published online August 1, 2012:2543-2565. doi:10.1210/jc.2011-2803
  6. Lazarus J, Brown RS, Daumerie C, Hubalewska-Dydejczyk A, Negro R, Vaidya B. 2014 European Thyroid Association Guidelines for the Management of Subclinical Hypothyroidism in Pregnancy and in Children. Eur Thyroid J. Published online 2014:76-94. doi:10.1159/000362597
  7. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid. Published online December 2014:1670-1751. doi:10.1089/thy.2014.0028
  8. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. Published online March 2017:315-389. doi:10.1089/thy.2016.0457
  9. Maraka S, Mwangi R, McCoy RG, et al. Thyroid hormone treatment among pregnant women with subclinical hypothyroidism: US national assessment. BMJ. Published online January 25, 2017:i6865. doi:10.1136/bmj.i6865

Date updated: 04.05.21 (V1.1)

Review date:   12.03.22

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