Hashimoto’s and early pregnancy

Design: BOOST Thyroid.

Design: BOOST Thyroid.

Experiencing the first trimester of pregnancy and/or miscarriage with an underactive thyroid

If you’ve become pregnant and you have an underactive thyroid and Hashimoto’s, it’s important to know how the thyroid affects the early stages of pregnancy. The thyroid is one of the most important organs in pregnancy. Being pregnant and having an underactive thyroid or Hashimoto’s can be challenging — an embryo needs thyroid hormones to develop, but cannot produce them on its own until the end of first trimester of pregnancy.

As an embryo depends on the mother’s thyroid hormones, it’s crucial to have enough hormones for your, and your baby’s, daily needs. If you are on thyroid medication, you will probably need to adjust the dose, possibly even more than once during the first weeks and months of pregnancy.

Here’s what to expect with hypothyroidism in the first three months of pregnancy (the first trimester):

Thyroid and embryo implantation

The embryo will implant in the uterus sometime between 2 and 8 days after ovulation (1).

Thyroid stimulating hormone (TSH) and T3 activate molecules necessary for the implantation of the embryo. The right levels of TSH, T4, and T3 are necessary for implantation to occur, as well as a good balance between T4 and T3 (2,3). After implantation has finished, the embryo will continue growing and the placenta will soon develop.

Thyroid and placenta development

The placenta brings essential nutrients to the growing embryo. This includes thyroid hormones, as the embryo doesn’t produce them yet. The placenta is made from the mother’s and baby’s DNA. An autoimmune condition also means a higher risk of a potential negative immune reaction against the cells of the placenta (4).

Thyroid and embryo development

Because the mother’s thyroid hormones T3 and T4 are vital for the development and function of the fetus and all its future organs, the thyroid gland needs to start producing significantly more hormones. TSH will increase, and the thyroid can double its size during pregnancy (5, 6).

Demand for T3 and T4 will grow until about the 10th or 11th week of pregnancy. After that, it will stay at that level during the rest of the pregnancy (7). The placenta will let more and more T4 through so it can further develop the embryo (7). The placenta contains special carrier molecules that transport thyroid hormones from the mother to the embryo. At about 11 weeks of pregnancy, the embryo starts producing its own thyroid hormones and the demand for the mother’s thyroid hormones drops (8–13).

Alongside supplying thyroid hormones to the growing embryo, the mother’s immune system must tolerate the embryo. To do so, the placenta serves as a barrier preventing the immune cells of the mother from reaching the embryo (14, 15).

Test your thyroid function before getting pregnant

According to the Endocrine Society guidelines, if you discover you’re pregnant or are planning a pregnancy, your doctor might want to run a full thyroid check up if you (16):

  1. Have a past history of thyroid disease or a part of a full thyroid was removed

  2. Have a family history of thyroid disease

  3. Have swollen neck (AKA goiter)

  4. Have elevated TPO or TG

  5. Have symptoms of an underactive thyroid, anemia, or hyponatremia

  6. Have type I diabetes

  7. Have other autoimmune disorders

  8. Had problems getting pregnant in the past, suffered a miscarriage, or had a preterm delivery

  9. Had your head or neck irradiated (therapeutic irradiation)

Pregnancy loss

Pregnancy loss can be both physically and emotionally challenging. While pregnancy loss is still at times an uncomfortable or even taboo topic to discuss publicly, early pregnancy loss is more common than previously thought (18). Statistics show that 3 in 10 pregnancies end in miscarriage, and out of those miscarriages 2 in 3 occur before the next period in the menstrual cycle (17).

Having unmanaged Hashimoto’s and an underactive thyroid increase the risk of early pregnancy loss, and chances of recurrent miscarriages are also increased (19- 21).

Pregnancy loss can happen as early as before or during the implantation process — which is before the next period would be due. People might only find out about some miscarriages if it happens repeatedly and they seek help from a fertility specialist (18).

What are the causes of miscarriage for people with hypothyroidism?

The American Association of Clinical Endocrinologists recommends measuring the antibodies TPO and TG if one has a history of repeated miscarriages and problems conceiving, and if one has subclinical hypothyroidism (22).

If TSH levels are between 2.5 mIU/L and 5.0 mIU/L in the first trimester — even without TPO or TG being detected — there is still an increased risk of an early pregnancy loss (23–256). In addition to TSH being above 2.5mIU/L, if TPO antibodies are detected, that may further increase the risk of an early pregnancy loss (27).

The two most common causes of an increased rate of early pregnancy loss are low thyroid hormones and an overactive immune system, which prevents thyroid hormones from reaching the embryo through placenta (28, 29).


  • Synthetic T4 (Synthroid or Levothyroxine)
    Treatment with the appropriate dose of synthetic T4 can reduce the risk of pregnancy loss by a third (30–32). The American Thyroid Association currently recommends treatment to start when TSH levels are above 4.0 mIU/L, or if TSH is above 2.5 mIU/L and TPO antibodies are detected (33).

    If you are already on T4 supplementation, your doctor might need to double your dose during early pregnancy (33). Use of iodine and iodine levels are a controversial topic, but it’s recommended to check your iodine levels as pregnancy increases the need for iodine, which is necessary for production of T4 and T3.

    Vitamin D levels should be well balanced, since vitamin D deficiency (<10 ng/mL) is connected to a higher risk of early pregnancy loss and a rise in the thyroid antibody levels (29).

  • Combination of synthetic T4 and T3
    There is a lack of research to understand how the combination of T3 and T4 impacts pregnancy. Researchers and medical doctors do not currently actively recommend using this combination. It can run the risk of T3 overmedication and an unnatural balance between T4 and T4, which can potentially lead to severe heart health problems (34).

  • Natural thyroid
    While natural thyroid preparations were used in the past — before synthetic T4 was available — there is no research on how it impacts pregnancy, or how it exposes patients to health risks.

    The main concern of researchers and medical doctors is the excessive amount of T3 relative to T4, making dosing very challenging. There is only one scientific report showing a patient using Armour Thyroid during pregnancy, with a full term delivery of a healthy baby. However, this isn’t scientific proof that this supplementation could work for all patients (35).

  • Helping your immune system
    Immunotherapy with the molecules immunoglobulins, especially in combination with heparin and Aspirin, may help reduce the risk of early pregnancy loss (36–38).

  • Selenium
    Selenium is essential for the thyroid to make T4 and T3 hormones. Selenium supplementation has been shown to reduce thyroid antibody levels during pregnancy (23).

  • Changing dosage of T4
    Be prepared to visit your doctor(s) more frequently and possibly take more blood tests. Doctors generally recommend to increase T4 by ¼ to ⅓ after a positive pregnancy test or a missed period (33).

As pregnancy puts a high demand on the thyroid, it’s beneficial to have your pregnancy in a controlled setting where your healthcare practitioner can monitor your thyroid function and your immune system together with your pregnancy.

Research is lacking some of crucial parts of thyroid treatment and pregnancy. BOOST Thyroid would like to investigate more and help both medical professionals and exploring thyroid treatment during pregnancy.

If you are interested in participating in a survey on this topic, please share your experience in this survey. We will publish the results in the coming months.


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  15. Aluvihare VR, et al. Regulatory T cells mediate maternal tolerance to the fetus, 2004

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  17. Kaprara A, et al. Thyroid autoimmunity and miscarriage, 2008

  18. Norwitz ER, et al. Implantation and the survival of early pregnancy. N Engl J Med, 2001

  19. Poppe K, et al. Thyroid disease and female reproduction, 2007

  20. Maraka S, et al. Subclinical hypothyroidism in pregnancy: a systematic review and meta-analysis, 2016

  21. van den Boogaard E, et al. Significance of (sub) clinical thyroid dysfunction and thyroid autoimmunity before conception and in early pregnancy: a systematic review, 2011

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  23. Negro R, et al. Increased pregnancy loss rate in thyroid antibody negative women with TSH levels between 2.5 and 5.0 in the first trimester of pregnancy, 2010

  24. Wang S, et al. Effects of maternal subclinical hypothyroidism on obstetrical outcomes during early pregnancy, 2012

  25. Schneuer FJ, et al. Association and predictive accuracy of high TSH serum levels in first trimester and adverse pregnancy outcomes, 2012

  26. Benhadi N, et al. Higher maternal TSH levels in pregnancy are associated with increased risk for miscarriage, fetal or neonatal death, 2009

  27. Liu H, et al. Maternal subclinical hypothyroidism, thyroid autoimmunity, and the risk of miscarriage: a prospective cohort study, 2014

  28. Pratt DE, et al. The association of antithyroid antibodies in euthyroid nonpregnant women with recurrent first trimester abortions in the next pregnancy, 1993

  29. Twig G, et al. Pathogenesis of infertility and recurrent pregnancy loss in thyroid autoimmunity, 2012

  30. Maraka S, et al. Thyroid hormone treatment among pregnant women with subclinical hypothyroidism: US national assessment, 2017

  31. Nazarpour S, et al. Effects of levothyroxine on pregnant women with subclinical hypothyroidism, negative for thyroid peroxidase antibodies, 2018

  32. Nazarpour S, et al. Effects of levothyroxine treatment on pregnancy outcomes in pregnant women with autoimmune thyroid disease, 2017

  33. Alexander EK, et al. 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum, 2017

  34. Wiersinga W, et al. 2012 ETA Guidelines: The Use of L-T4 + L-T3 in the Treatment of Hypothyroidism, 2012

  35. https://www.endocrine-abstracts.org/ea/0038/eposters/ea0038P486_eposter.pdf

  36. Kiprov DD, et al. The use of intravenous immunoglobulin in recurrent pregnancy loss associated with combined alloimmune and autoimmune abnormalities, 1996

  37. Stricker RB, et al. Successful treatment of immunologic abortion with low-dose intravenous immunoglobulin, 2000

  38. Sher G, et al. The use of combined heparin/aspirin and immunoglobulin G therapy in the treatment of in vitro fertilization patients with antithyroid antibodies, 1998