Impact of hypothyroidism on pregnancy and the baby?

Dear Alice,

I am a bit confused about conceiving as I have a low thyroxine level. What impact might it have on pregnancy and the baby?


want to be a mother

Dear want to be a mother, 

Low thyroxine levels, also known as hypothyroidism or an underactive thyroid, occur when the thyroid gland doesn’t produce enough hormones. Typically, a medical professional will evaluate the functioning of the thyroid gland using a common blood test called TSH (thyroid-stimulating hormone) test. A TSH test measures the levels of thyroid hormones circulating in the blood and serves as a guide to determine if the thyroid is functioning properly. Thyroxine (T4) is the main hormone produced in the thyroid gland, along with triiodothyronine (T3). These thyroid hormones help to keep metabolism, body temperature, heart rate, and protein production under control. If someone has low thyroxine levels, it often means that their thyroid gland isn’t producing enough T4, which can lead to hypothyroidism. But what impact can this have on pregnancy and a baby you ask? Complications like infertility, birth defects, and higher risks of miscarriage may occur due to a lower thyroxine level. However, you can still have a healthy pregnancy and protect your baby’s health by having regular thyroid function tests and taking specific medications that a medical professional prescribes (more on this later). 

Some factors that contribute to low hormone levels include thyroiditis (the inflammation of the thyroid gland) and medications such as lithium, and radiation therapy. The most common cause of hypothyroidism is an autoimmune disease called Hashimoto’s disease, a disorder in which the immune system attacks the thyroid gland. Hashimoto’s can affect fertility by interfering with ovulation, which occurs when an egg is released from the ovary. This can make conception especially difficult. For those who do conceive, and continue to live with untreated low levels of thyroxine, they may be at greater risk of the following during pregnancy: 

  • Miscarriage 
  • Premature birth 
  • Maternal anemia 
  • Muscle pain 
  • Pre-eclampsia 
  • Congestive heart failure 
  • High blood pressure 
  • Postpartum hemorrhage 
  • Structural placental anomalies 

List adapted from the American Thyroid Association 

If left untreated during pregnancy, Hashimoto’s can also significantly impact the development of your baby. Children born under these conditions may be born with a defective thyroid gland, leading to thyroid hormone deficiency (also known as congenital hypothyroidism). The thyroid hormone is critical for brain development in early life. Its deficiency can lead to impaired brain development, which can lead to severe cognitive, neurological, and developmental conditions. 

Fortunately, treating hypothyroidism under the supervision of a health care provider increases the likelihood of conception and a safer pregnancy. Hypothyroidism is typically treated with a thyroid hormone medicine which works by increasing levels of thyroid hormones in the body during pregnancy. Discussing your TSH levels with a health provider can help you further explore treatment guidelines. For individuals who are unsure if they have hypothyroidism and are trying to get pregnant, it may be best to reach out to a health care provider to get blood tests measuring TSH levels. 

Receiving appropriate treatment for hypothyroidism as early as possible under the close supervision of a health care provider is just one way to prevent health complications between a pregnant person and their child. Best of luck to you as you begin this exciting new journey! 

Last updated Aug 18, 2023
Originally published Feb 20, 2015

Submit a new comment


This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

The answer you entered for the CAPTCHA was not correct.