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The Butterfly Effect: Thyroid Imbalances

The Butterfly Effect: Thyroid Imbalances

Thyroid glands are an important part of the endocrine system for both mother and baby. These glands control specific processes, including growth and energy release.6 

Thyroid: What Is It and Why Is It Important? 

The thyroid is a small, butterfly-shaped gland at the front of your neck under the skin that creates and delivers the thyroid hormone. The thyroid hormone controls your weight, body temperature, etc.2The thyroid hormone consists of thyroxine (T4) and triiodothyronine (T3). Although they are two different hormones, they are named the “thyroid gland” because T4 does not impact your cells meaning it is inactive while T3 is active. Although T4 is inactive, it is still needed to produce T3. They are both equally important hormones within the body.1 

How does your Thyroid Affect Fertility and Pregnancy?

Thyroid hormones are essential to brain development and the nervous system in babies. Babies depend on the thyroid hormone during the first trimester or the first three months of your pregnancy. At the end of the first trimester, approximately week 12 of pregnancy, your baby’s thyroid will begin working on its own. However, it does not make enough thyroid hormone until weeks 18-20 of pregnancy. 3 


Hypothyroidism, often called underactive thyroid, is a condition that happens when the thyroid gland is not making enough thyroid hormone. The common symptoms associated with hypothyroidism include: 

  • Tiredness 
  • Constipation 
  • Muscle aches, tenderness and stiffness 
  • Menstrual cycles that are heavier than usual or irregular 
  • Slowed heart rate (bradycardia) 

Hypothyroidism does not always cause noticeable signs and/or symptoms in the early stages. If it is not treated, it can lead to other health problems such as high cholesterol and some heart problems. There are a few conditions/ problems that can lead to hyperthyroidism such as: 

  • Autoimmune Disease 

Autoimmune diseases occur when antibodies attack healthy tissues. Hashimoto’s disease is the most common autoimmune disease that can cause hypothyroidism. 

  • Thyroiditis 

When the thyroid gland is inflamed, it is called thyroiditis. This could be caused by an infection, autoimmune disorder, or another medical condition. 

  • Radiation therapy 

Radiation is a common therapy treatment for head and neck cancers. The radiation from those treatments can negatively affect the thyroid gland and lead to hypothyroidism.4 

How does Hypothyroidism Affect Fertility, Pregnancy, and My Baby?

When hypothyroidism is left untreated during the first trimester, problems with development can occur. In more severe cases, the following problems often occur: 

  • Preeclampsia 

Preeclampsia is an unhealthy spike or rise in blood pressure during the late stages of pregnancy. 

  • Anemia 

Anemia is a condition in which your red blood cell count is lower than the recommended count. This is concerning because red blood cells transfer oxygen from the lungs to your tissues. 

  • Miscarriage 
  • Low birthweight 
  • Stillbirth 
  • Congestive heart failure 

Congestive heart failure happens when your heart slows down or loses its power to pump which causes fluid to build up.3 

Sometimes there is a link between infertility and hypothyroidism. When low levels of thyroid hormone get in the way of ovulation, when an egg is released from your ovary, infertility can occur. Certain autoimmune disorders associated with hypothyroidism also have the ability to cause infertility.5 

Treatment for Hypothyroidism during Pregnancy 

After a blood test is taken to confirm problem(s) with thyroid hormone levels, your healthcare provider may prescribe thyroxine tablets. These tablets are used for an underactive thyroid (hypothyroidism) as a form of hormone replacement. If this prescription does not work, a part or all the thyroid can be removed through surgery. Another option is radioactive iodine to target and kill active thyroid cells.6Consult your healthcare provider to discuss the best option for you. 


In contrast to hypothyroidism, hyperthyroidism is an overactive thyroid. Too much T4 and T3 is released causing your metabolism to speed up in a dangerous manner. Symptoms of hyperthyroidism include: 

  • Rapid pulse 
  • Tremor (shaking) of the hands 
  • Sweating and sensitivity to heat 
  • Nervousness, agitation and anxiety 

If left untreated, hyperthyroidism can lead to liver damage, heart failure and possibly death.6 

How does Hyperthyroidism Affect Fertility, Pregnancy, and My Baby? 

Hyperthyroidism caused by Graves’ disease occurs in 1-4 of every 1,000 pregnancies in the US. Graves’ disease can first appear in pregnancy but if you already have Graves’ disease, symptoms can improve within the second and third trimesters. This is possibly due to parts of the immune system being less active during pregnancy. In rare cases, hyperthyroidism in pregnancy is connected to severe nausea and vomiting, a condition called hyperemesis gravidarum, which leads to weight loss and dehydration. 

Untreated hyperthyroidism in pregnancy can lead to: 

  • Premature birth 
  • Low birthweight 
  • Miscarriage 
  • Preeclampsia 
  • Congestive heart failure 
  • Thyroid storm 

Treatment for Hyperthyroidism during Pregnancy?

A mild case of hyperthyroidism more than likely will not require treatment. If your hyperthyroidism is causing severe nausea and vomiting, then there will be treatment for vomiting and dehydration. For more severe cases of hyperthyroidism, your healthcare provider may provide medication during your first trimester that blocks too much thyroid hormone from getting into your baby’s bloodstream. It is recommended that you see an endocrinologist or an expert in maternal-fetal medicine to monitor the baby to ensure you’re getting the proper dose of your medication. 3 

Postpartum Thyroiditis 

Postpartum thyroiditis occurs when the thyroid gland is inflamed after having a baby. This is a rare occurrence affecting 3 in 100 to 2 in 25 pregnancies. Postpartum thyroiditis first makes your thyroid overactive but eventually leads to an underactive thyroid overtime. You may be more likely to develop this condition if you: 

  • Have antithyroid antibodies before pregnancy 
  • Have type 1 diabetes 
  • Have a history of thyroid problems 
  • Have a family history of thyroid problems 

Some symptoms of postpartum thyroiditis could be: 

  • Muscle weakness 
  • Nervousness, anxiety 
  • Fast heartbeat 
  • Loss of focus 
  • Fatigue 
  • Constipation 
  • Memory loss 

It is possible that your symptoms do not occur until months after giving birth. Many of these symptoms are thought to be normal signs of recovery. Consult your healthcare provider to obtain a proper diagnosis. 

If you are diagnosed with postpartum thyroiditis there are a few treatment options based on the phase of thyroid disease and specific symptoms. For those with an overactive thyroid you may be prescribed beta blockers and/or prednisone to slow the heart rate and reduce inflammation. If you are suffering from an underactive thyroid your healthcare provider may prescribe thyroid hormone replacement. 7 

While these thyroid problems are possible, you can have a healthy pregnancy and a healthy baby by regularly taking thyroid function tests and taking medications that your healthcare provider prescribes.3

Written by: Taylor Neither, MPH

Blog Expertly Reviewed by: Dr. Krista Mincey, MPH, Dr.PH, MCHES
  1. Cleveland Clinic. (2022).
  2. Cleveland Clinic. (2021).
  3. NIH. (2017).,medicines%20that%20your%20doctor%20prescribes 
  4. Mayo Clinic. (2022). 
  5. Mayo Clinic. (2023). -and-infertility/faq-20058311#:~:text=Low%20levels%20of%20thyroid%20hormone,pituitary%20disorders%20%E2%80%94%20may%20impair%20fertility 
  6. Better Health. (2015). 
  7. Johns Hopkins Medicine. 
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