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Early Pregnancy, Hypothyroidism, and Hashimoto’s

Early diagnosis and treatment of hypothyroidism and Hashimoto’s in pregnancy is crucial for a healthy outcome.
Early Pregnancy, Hypothyroidism, and Hashimoto’s
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Pregnancy is a transformative and exciting time in your life, but it can also be a time of health challenges and important considerations. When you are pregnant, preexisting hypothyroidism or Hashimoto’s disease can pose extra challenges. Both conditions involve the thyroid gland, which regulates metabolism and supports a healthy pregnancy. As such, managing thyroid health during pregnancy – especially the earlier stage – is essential for the well-being of both the mother and the developing baby. In this article, we will explore some of the critical issues around hypothyroidism and Hashimoto’s in early pregnancy and discuss the importance of proper management and care to ensure a healthy and successful pregnancy journey.

Why is thyroid hormone so crucial during the first trimester?

First, it’s essential to know why the first trimester is so important for women with hypothyroidism or Hashimoto’s. The embryo needs thyroid hormones to develop properly, but it can’t produce them on its own until the end of the first trimester of pregnancy. Until then, the embryo depends on the mother’s thyroid hormones for all its needs. This means the pregnant woman must have enough hormones for her and her developing baby’s daily needs.

If you are on thyroid medication, you should plan to retest your thyroid levels as soon as pregnancy is confirmed. Also, be aware that you will probably need to increase your dose, possibly even more than once, during the first weeks and months of pregnancy.

TSH ranges during pregnancy

The reference ranges for thyroid-stimulating hormone (TSH) during pregnancy vary by trimester due to physiological changes that occur to support both the mother and the developing fetus. Using trimester-specific reference ranges is vital because the normal range for TSH changes throughout pregnancy. These ranges are influenced by factors such as gestational age, analytical methods used for measurement, and the population being studied, including ethnicity and iodine intake. There’s also a consensus that non-pregnant TSH reference intervals should not be applied to pregnant women due to these physiological changes.

The American Thyroid Association (ATA) guidelines recommend a TSH range of 0.1–2.5 mIU/L for the first trimester. However, numerous studies suggest a more realistic upper limit may be between 2.30 and 4.0 mIU/L, depending on the population and methodology used. Another study recommends that the upper limit be 3.52 mU/L in the first trimester, aligning with European and American findings.

For the second trimester, the ATA guidelines suggest a TSH range of 0.2–3.0 mIU/L. However, research indicates that the upper limit can vary, with one study reporting a range of 0.47 to 3.89 mIU/L, suggesting that the upper limit can be higher than the ATA’s recommendation.

In the third trimester, the ATA guidelines recommend a TSH range of 0.3–3.5 mIU/L. Research findings show a range of 0.55 to 4.91 mIU/L in one study, and another study reported an upper limit of 3.67 mU/L, indicating variability in the upper limit of the normal range.

Given the variability in TSH reference ranges across different studies, you and your doctor should use local, trimester-specific reference ranges for TSH during pregnancy. These ranges should ideally be based on the population being served, considering factors such as ethnicity, iodine intake, and the specific assays used. If local reference ranges are unavailable, guidelines from reputable organizations like the ATA can be used, keeping in mind that adjustments may be needed based on the latest research.

How does the thyroid function during early pregnancy?

An embryo implants in the uterus sometime between 2 to 8 days after ovulation and fertilization. Thyroid stimulating hormone (TSH) and the thyroid hormone triiodothyronine (T3) activate molecules necessary for embryo implantation. The right levels of TSH, T3, and thyroxine (T4) are essential for implantation to occur, as well as a good balance between T4 and T3. After implantation, the embryo will continue growing, and the placenta will soon develop.

The placenta brings essential nutrients to the growing embryo. This includes thyroid hormones because, as outlined earlier, the embryo can’t produce them yet.

Because the mother’s T3 and T4 thyroid hormones are vital for the development and function of the embryo and all its future organs, the mother’s thyroid gland needs to start producing significantly more hormones. TSH will increase, and a healthy thyroid gland can double its size during pregnancy to meet the demand for more thyroid hormone.

This demand for T3 and T4 grows until about the 10th or 11th week of pregnancy. After that, it tends to stay at that level during the rest of the pregnancy. The placenta will let more and more T4 through to further support the embryo’s development. 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 decreases.

In addition to supplying thyroid hormones to the growing embryo, the mother’s immune system must tolerate the embryo. The placenta accomplishes this by serving as a barrier that prevents the mother’s immune cells from reaching the embryo.

When should you test your thyroid?

‍A study in the Journal of Applied and Basic Medical Research found that 2-4% of women in the reproductive age group have low thyroid hormone levels.  This thyroid dysfunction may result in irregular menstrual cycle patterns, abnormal endometrial development, high prolactin levels, or sex hormone imbalances. All of these can affect fertility and pregnancy outcomes.

According to the Endocrine Society’s guidelines, if you are planning a pregnancy or you discover you’re pregnant, thyroid testing is recommended if you:

  • Have symptoms of an underactive thyroid
  • Have symptoms of anemia or hyponatremia
  • Have a personal history of thyroid disease
  • Have a personal history of autoimmune disease
  • Have a family history of thyroid disease or autoimmune disease
  • Have a swollen neck or enlarged thyroid (goiter)
  • Have elevated thyroid peroxidase (TPO) or thyroglobulin (Tg) antibodies
  • Have a history of irregular periods
  • Haven’t conceived after one year of unprotected sex
  • Have type I diabetes
  • Have had problems getting pregnant in the past, suffered a miscarriage, or had a preterm delivery
  • Have had radiation treatment to your head or neck

This thyroid evaluation should include TSH, T4, T3, and TPO antibodies. Thyroid antibodies are not always included in the initial fertility workup, though it is important because their presence affects the risk of recurrent miscarriage.

What are the symptoms of hypothyroidism in pregnancy?

The symptoms of hypothyroidism and Hashimoto’s during pregnancy can be similar to those in non-pregnant individuals. It’s essential, however, to recognize and manage thyroid issues that develop or worsen during pregnancy because they can potentially impact both the mother and the developing baby. The common symptoms of hypothyroidism and Hashimoto’s during pregnancy include:

  • Feeling tired
  • Inability to tolerate cold temperatures
  • Depression
  • Hoarse voice
  • Sensitivity in the throat or neck
  • Neck or thyroid enlargement (goiter)
  • Swelling of the face
  • Weight gain
  • Constipation
  • Skin changes, including dry, rough skin
  • Hair loss, including loss of the outer edge of the eyebrows
  • Brittle nails
  • Carpal tunnel syndrome (hand tingling or pain)
  • Slow heart rate
  • Muscle cramps, weakness, joint pain
  • Trouble concentrating, slowed thinking, “brain fog”
  • Peripheral neuropathy (numbness and tingling in the extremities)
  • Depression and anxiety
  • Changes in blood pressure

It’s important to note that not all women with hypothyroidism may experience noticeable symptoms, and some symptoms of hypothyroidism may be mistaken for normal pregnancy discomforts. Therefore, pregnant women need to undergo routine screening if they have symptoms of hypothyroidism, a history of the condition, or other endocrine system conditions.

How can you reduce the risk of pregnancy loss?

Pregnancy loss can be both physically and emotionally challenging. Early pregnancy loss is more common than previously thought. 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.

Having unmanaged Hashimoto’s and hypothyroidism also increases the risk of early pregnancy loss, as well as the risk of recurrent miscarriages.

If TSH levels during the first trimester of pregnancy are within the reference range but in the upper half of the non-pregnant range -- between 2.5 mIU/L and 5.0 mIU/L -- there is still an increased risk of an early pregnancy loss, even without TPO or Tg antibodies present. 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.

These findings underscore the importance of following the pregnancy-specific TSH ranges discussed earlier.

Managing hypothyroidism or Hashimoto’s during pregnancy

Treatment with the appropriate dose of levothyroxine (synthetic T4) to maintain levels within the pregnancy-specific range can help ensure a healthy pregnancy. In addition, treatment can reduce the risk of pregnancy loss by as much as a third. The ATA currently recommends treatment starting when TSH levels are above 4.0 mIU/L or if TSH is above 2.5 mIU/L and TPO antibodies are detected.

If you are already on T4 supplementation, your doctor might need to double your dose during early pregnancy. The use of iodine and testing of iodine levels are controversial. Still, it’s recommended to check your iodine levels as pregnancy increases the need for iodine, which is necessary to produce T4 and T3.

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

The mineral selenium is also essential for the thyroid to make T4 and T3 hormones. Selenium supplementation has been shown to reduce thyroid antibody levels during pregnancy.

In some women with Hashimoto’s, research shows that immunotherapy with immunoglobulins, especially in combination with heparin and aspirin, may help reduce the risk of early pregnancy loss.

Finally, because early pregnancy puts a high demand on the thyroid, and thyroid hormone is essential to the developing baby during the first trimester, it’s crucial to ensure your thyroid function is carefully monitored before and during pregnancy.  

A note from Paloma

Preparation, early detection, and management of hypothyroidism and Hashimoto’s thyroiditis during early pregnancy are crucial for ensuring the health and well-being of both the mother and the developing baby. Regular monitoring of thyroid function, appropriate medication adjustments, and close collaboration between the patient, obstetrician, and thyroid practitioner are essential in optimizing outcomes. By staying informed, proactive, and adhering to medical advice, women with these conditions can navigate pregnancy successfully, reducing potential risks and complications. With proper care and support, women can look forward to a healthy pregnancy and a positive start to motherhood.

One way to make the process easier is the Paloma Complete Thyroid Test kit. This at-home test allows you to collect and analyze a blood sample conveniently, measuring key biomarkers such as TSH, Free T3, Free T4, and TPO antibodies. The comprehensive report indicates whether these markers fall within normal healthy ranges. The kit is suitable for both diagnosed hypothyroid patients and those seeking to understand their thyroid function better. With the ease of testing from home, quick results, and the ability to track changes over time, the Paloma Health test kit provides a convenient and informative way to monitor thyroid health.

Vedrana Högqvist Tabor, Ph.D., and Julia Walker, RN, BSN, contributed to this article.


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Mary Shomon

Patient Advocate

Mary Shomon is an internationally-recognized writer, award-winning patient advocate, health coach, and activist, and the New York Times bestselling author of 15 books on health and wellness, including the Thyroid Diet Revolution and Living Well With Hypothyroidism. On social media, Mary empowers and informs a community of more than a quarter million patients who have thyroid and hormonal health challenges.

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