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How Thyroid Function Affects Pregnancy

How Thyroid Function Affects Your Pregnancy

There are many factors involved in safeguarding the early development of an unborn child during pregnancy. One of the most influential being hormone balance. Sadly, many are not aware of the powerful impact that hormones, specifically thyroid hormones, have during the early stages of pregnancy. Worse still many mothers are not aware of existing thyroid issues that can lead to pregnancy issues such as developmental disorders, physical defects, and even loss. Recognizing the critical role of thyroid hormones and taking the appropriate steps to keep them balanced is essential for healthy pregnancies.

The Influence of Thyroid Hormones During Pregnancy

Thyroid hormones play an important role in fetal development. The hormones coordinate the many genetic factors ranging from neurological development to physical attributes that are necessary for the creation of a new life. When levels are low or depleted, the body’s genetic programming cannot be completed properly thereby increasing the risk of birth defects. The brain in particular is sensitive to decreased thyroid levels during early development. Therefore, a deficiency of thyroid hormone significantly increases the risk of poor brain development in the unborn child.

In the early stages of pregnancy, specifically the first trimester, the fetus is entirely reliant on the mother for thyroid hormones. Multiple studies have shown that even marginally low levels in pregnant women can lead to neurological issues including poor cognitive function in their newborn. Therefore, maintaining healthy levels of thyroid hormones in both the mother and child is essential for the child’s wellness and development.

The Impact of Hypothyroidism on Pregnancy

Significant deficiencies of thyroid hormone caused by hypothyroidism or other thyroid disorders can result in prominent pregnancy issues. Hypothyroidism is a reduction of thyroid activity resulting in a deficit of thyroid hormones. It is common for those with undiagnosed hypothyroidism to recognize their condition during the first trimester of pregnancy because this is when the demand for thyroid hormone is at its highest. It is common for those with hypothyroidism, and occasionally those with healthy thyroid function, to be administered supplementary thyroid replacement medication to help keep up with the additional demand from the newly forming child and their own body.

Typically, during pregnancy the mother’s thyroid gland increases in size to support greater production of the requisite hormones. Unfortunately, hypothyroidism can impede this bodily adaptation and disrupt the pregnancy. Maternal hypothyroidism, especially if it is untreated, is associated with various pregnancy complications including: postpartum hemorrhage, placental abruption, preterm labor, miscarriage, still birth, maternal anemia, pre-eclampsia, premature delivery, low birth weight, and greater risk of physical and developmental deficiencies in the child.

The Early Influence of Thyroid Hormones

Maintaining proper hormone balance through the entire pregnancy is important for the healthy development of the child. However, during the first trimester, hormone balance is crucial regarding fetal development. Cell nuclei contain between 2,000 to 10,000 thyroid hormone receptors meaning that thyroid hormone levels and function have an impressive influence over early development.

The requirement for thyroid hormone is at its height during the first trimester. Animal studies have shown that the first half of pregnancy may be a period of increased sensitivity wherein a lack of thyroid hormone can significantly disrupt neurogenesis, promote neuronal migration errors, and inhibit brain development in the fetus. Thyroid hormones also impact placental trophoblasts, which influence blood flow and nutrient delivery to the newly forming fetus. Deficiency in this area can further disrupt fetal development. Because of this, it is important that thyroidal intervention and care be administered during the first trimester of pregnancy. After about 16 weeks hormone values typically normalize but thyroid support may still be required for mothers with a thyroid condition.

The Risk of Deficiency During Pregnancy

It is estimated that between 3-10% of women have hypothyroidism meaning that the risk of disrupted fetal development during pregnancy due to thyroid dysfunction is relatively high. TSH is the most common metric used for assessing thyroid function. Guidelines provided by the American Thyroid Association states that TSH levels should not be above 2.5 during the first trimester and no more than 3.0 during the second and third trimester.

One study composed of over 50,000 hypothyroid women showed that during the first trimester nearly 63% of the participants had a TSH near the upper limit of 2.5, which is indicative of hypothyroidism. Over 7% of participants had TSH levels above 10. This is highly irregular and suggests severe thyroidal dysfunction. The researchers found that women who had a TSH above 4.51 showed an increased risk for miscarriage as opposed to those who had a TSH between 0.2 and 2.5 during the first trimester. Although TSH is not an infallible method of identifying thyroid dysfunction, at significantly elevated levels it does suggest thyroidal dysfunction that could negatively affect pregnancy.

Testing for Maternal Hypothyroidism

An undiagnosed thyroid issue could contribute significantly to development issues in a developing child. Identifying thyroid dysfunction or deficiency before pregnancy and subsequently treating it is the best way to avoid potential thyroid-related pregnancy issues. Sadly, there is no standardized or required thyroid screening for women who are pregnant. However, requesting a pre-conception evaluation to assess levels of thyroid hormones such as TSH, Free T4, Free T3, and thyroid antibodies such as Thyroid Peroxidases (TPO) can help identify an existing thyroid disorder or irregularity. Doing so may support the pregnancy and help protect the early development of the unborn child. It is important to regularly reevaluate thyroid function during the first trimester as this is when the risk of pregnancy-related thyroid dysfunction is greatest.

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Doing Thyroid Diligence to Protect Pregnancy

Irregular thyroid function may impede and disrupt pregnancy. Therefore, it is crucial to have the thyroid tested before conception and regularly assessed during the first trimester. After the first trimester when hormone levels have stabilized testing intervals can be reduced. If any issues develop, it is critical to get the appropriate care and treatment to stabilize thyroid function and hormone levels. Identifying and resolving thyroid issues prior to pregnancy reduces the risk of complications and helps ensure that fetal development is safeguarded throughout the term. Protect your pregnancy by supporting your thyroid.


1. Thyroid Hormone, Birth Defects, and the Developing Brain. Hypothyroid Mom.

2. What Every Pregnant Woman Needs To Know About Hypothyroidism. Hypothyroid Mom.

3. Why You Need Thyroid Tests Before You Get Pregnant. Holtorf Medical Group.

4. Hypothyroidism in Pregnancy: Get Your Thyroid Levels Adjusted Before Getting Pregnant. Holtorf Medical Group.

5. Should You Increase Your Thyroid Medication During Pregnancy? Holtorf Medical Group.

6. Exploring the Link between Premature Births & Maternal TSH Levels. Holtorf Medical Group.

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