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Hypothyroidism and Pregnancy

Early diagnosis and treatment of hypothyroidism in pregnancy is critical.
Hypothyroidism and Pregnancy
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In this article:

  • How can hypothyroidism affect fertility?
  • What are the symptoms of maternal hypothyroidism?
  • How can hypothyroidism affect the baby?
  • How do doctors treat hypothyroidism in pregnancy?
  • What is postpartum thyroiditis?
  • Postpartum follow-up


Hypothyroidism is caused by an underactive thyroid gland. When your thyroid hormone production drops, your body processes slow down and change. Hypothyroidism can affect many different systems in your body.

To cope with the metabolic demands of pregnancy, the mother's thyroid gland undergoes noticatable modifications. These changes are reversible post-partum.

However, undiagnosed thyroid disease may put patients at risk for other pregnancy-related problems. These problems may include changes in menstruation, infertility, or miscarriage.

How can hypothyroidism affect fertility?

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.

As such, normal thyroid function is necessary for fertility and a healthy pregnancy. You should test your thyroid function if:

  • You plan to get pregnant, 
  • Have a history of thyroid problems or irregular periods,
  • Have miscarried
  • Are unable to conceive after one year of unprotected sex.

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 may double the risk of recurrent miscarriage.

What are the symptoms of hypothyroidism in pregnancy?

Hypothyroidism is a common condition that can go undetected if symptoms are mild or nonexistent. 12% of the US population has a thyroid disorder, and 60% don’t know about it. This underdetection is especially true during pregnancy when many symptoms of hypothyroidism attributes to pregnancy.

Hypothyroidism may be present if you have symptoms like: 

  • Slowed thinking or mental activity (“brain fog”)
  • Thinning hair or eyebrows
  • Peripheral neuropathy
  • Mental health issues
  • Goiter (enlarged thyroid gland)
  • High blood pressure
  • Intolerance to cold
  • Weight gain
  • Stomach bloating
  • Heartburn
  • Constipations
  • Irregular or heavy menstrual periods
  • Weak or achy muscles
  • Dry or rough skin

Always talk with your medical care team for a diagnosis.

How can hypothyroidism affect the baby?

During pregnancy, the baby relies on the mom for thyroid hormones that support healthy brain development and growth. Hypothyroidism in the mom can disrupt this stage of development that may have long-lasting effects. 

Untreated hypothyroidism may result in premature birth, low birth weight, or respiratory issues in the newborn. Evidence also shows that the thyroid hormone thyroxine (T4) is vital to the healthy development of the fetal brain.

Additionally, a study from the Journal of Clinical Endocrinology and Metabolism suggests that babies born to moms with an iodine deficiency may have a slight deficit in IQ or be prone to attention deficit hyperactivity disorder. Not only is iodine necessary to make thyroid hormones, the liver actually requires it to convert thyroxine (T4) to triiodothyronine (T3). 

How do doctors treat hypothyroidism during pregnancy?

A pregnant woman experiences an enormous increase in estrogen during pregnancy, which helps the uterus and placenta to support the developing baby, improve the formation of blood vessels, and transfer nutrients.

Estrogen levels reach their peak in the third trimester of pregnancy. This significant rise in estrogen levels causes an increase in thyroxine-binding globulin (TBG) levels. TBG is a protein that helps to move thyroid hormones throughout your body. 

Pregnant women with hypothyroidism are typically treated with levothyroxine, a thyroid hormone replacement drug. Pregnant women may need larger doses due to the rise in TBG. Dosage depends on each mom’s thyroid hormone levels, in addition to her symptoms.

Thyroid hormone levels will likely change during pregnancy, and as such, the hormone replacement dose will change with them. An expecting mom should test their thyroid hormone levels every month in the first half of pregnancy and may be checked less often during the second half of pregnancy. 

Hormone replacement is safe for both mother and baby. However, Stanford Children’s Health suggests that these drugs should not be taken at the same time as prenatal vitamins to support absorption.

To minimize the risk of complications, pregnant women should work closely with an obstetrician and endocrinologist to monitor hormone levels. All treatment should be under the care of a doctor. 

What is postpartum thyroiditis?

Postpartum thyroiditis is an inflammation of the thyroid that affects about 5% of women in the first year after giving birth. Sometimes post-partum thyroiditis is mistaken for the “baby blues” - a mild depression or mood swings that new mothers sometimes experience after the baby is born. It may develop by a mild form of autoimmune thyroiditis that flares up after you give birth. You should talk to your doctor as soon as possible if you experience these symptoms. 

Postpartum Follow-Up

After the delivery of the baby, many women will be able to decrease their hormone replacement dosage received during pregnancy over approximately four weeks. It is beneficial to self-monitor symptoms and share any concerns with your doctor to maintain optimal thyroid function. 

In conclusion, when a thyroid condition is detected early in pregnancy, it is easy to treat with minimal impact on mom and baby


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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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