FAQ: Thyroid & Pregnancy

by Yumhee Park Content Producer

The thyroid, a butterfly shaped gland located in your neck, regulates your metabolism. When problems occur in the thyroid it can throw your whole body off balance. Women are statistically more likely to suffer from it than men, and for women looking to get pregnant, thyroid problems could be dangerous for pregnancy.

HealthCentral covered some frequently asked questions about thyroid and pregnancy with Elizabeth Pearce, MD. Elizabeth is currently co-chairing the American Thyroid Association‘s Thyroid and Pregnancy Clinical Guidelines Task Force. She is also an endocrinologist and Associate Professor of Medicine at the Boston University School of Medicine.

HealthCentral (HC): What should a first-time mother with a known thyroid disease be concerned about regarding her thyroid?

Elizabeth Pearce, MD: The most common form of thyroid disease is hypothyroidism, or underactive thyroid. Women of child-bearing age who are being treated with thyroid hormone for hypothyroidism prior to pregnancy should be aware that their dose of thyroid hormone almost always needs to increase once they become pregnant. Thyroid hormone is essential for normal neuro-development of the fetus. Increasing the dose as early in pregnancy as possible is vital. Many doctors recommend that a woman who is treated with thyroid hormone prior to pregnancy should automatically increase the thyroid hormone dose by two tablets a week (if she usually takes one tablet a day). It’s important that women contact their care provider as soon as they find out they are pregnant.

HC: What about first-time mothers who may not know that they have a thyroid problem? How is the thyroid affected during pregnancy, exactly?

Elizabeth Pearce, MD: The thyroid increases its function naturally during pregnancy, so normally, assuming a woman is healthy and her thyroid is functional, she will increase her thyroid hormone production by about 50% starting early in pregnancy. Therefore, pregnancy acts as a stress test for the thyroid gland.

It's controversial whether all healthy women should have screening for thyroid function in early pregnancy or not. Current guidelines on the topic are mixed, with some medical societies advocating no testing, some advocating for universal testing, and some advocating for testing only in high-risk women. If we were to test for thyroid function in every pregnant woman we would detect mildly low thyroid function in some of them.

HC: What is mildly low thyroid function?

Elizabeth Pearce, MD: Mildly low thyroid function is called subclinical hypothyroidism. It is diagnosed on the basis of laboratory testing: in subclinical hypothyroidism the blood thyroid stimulating hormone (TSH) level is elevated but the actual thyroid hormone levels are normal. Outside the setting of pregnancy, it's controversial whether or not treatment is required. Most people who have mildly low thyroid function don't have symptoms, although, there may be subtle symptoms if you look at enough people and ask the questions carefully enough.

HC: Are there other ways how hypothyroidism affects the mother and the developing fetus if a woman is pregnant with hypothyroidism?

Elizabeth Pearce, MD: Severe hypothyroidism in pregnancy definitely has adverse effects; there are higher rates of prematurity, miscarriage, and congenital anomalies and there are adverse effects on child cognitive development. Overt hypothyroidism should always be treated. Whether or not mild maternal hypothyroidism needs to be treated is more controversial.

HC: I see. Are there efforts being made to conduct more in-depth studies about how interventional methods might benefit or might not benefit?

Elizabeth Pearce, MD: Results of the Controlled Antenatal Thyroid Screening (CATS) were published in the New England Journal of Medicine in 2012. In that study, some women with mildly low thyroid function in pregnancy were randomly assigned to treatment with thyroid hormone. Child IQ was assessed at the age of three, and there was no difference in IQ between the children of the treated and untreated mothers. There's a very similar study currently ongoing in the U.S. – a big NIH multi-center study. The results of the NIH study will be announced in 2016. There is currently also a large clinical trial examining the effects of testing for and treating mild maternal hypothyroidism which is ongoing in China.

HC: How important do you think it is for women, who are trying to get pregnant, to check that their thyroid is in working order? Do you think that it is an essential test or if they don't have any symptoms, they just shouldn't get it checked? What are your thoughts on that?

Elizabeth Pearce, MD: The most recent guidelines from the American Thyroid Association for thyroid and pregnancy date from 2011. I was an author on those guidelines. We are currently writing a revision to those guidelines, which will be out next year.

In the previous guidelines, we recommended a case finding strategy. We felt that there wasn't really enough evidence to recommend for testing thyroid function in every single pregnant woman, unless she had risk factors.

Risk factors from the previous guidelines include:

  • Women with a known history of thyroid problems

  • Women with a family history of thyroid disease

  • Women with thyroid enlargement

  • Women who have detectable antibodies against the thyroid in the blood

  • Women with symptoms that suggest hypothyroidism

  • Women with Type 1 Diabetes, because the risk of hypothyroidism is higher

  • Women with a history of miscarriage or pre-term delivery, because hypothyroidism can be associated with those things

  • Women with other autoimmune disorders

  • Women with a history of infertility should have screenings because thyroid problems can be one cause of infertility that might be treatable

  • Women with a history of morbid obesity (A BMI greater than 40)

  • Women age 30 or older

HC: Do you know if birth control usage affects the thyroid at all?** Elizabeth Pearce, MD:** Birth control use does not affect thyroid function. However, when a woman starts or stops a birth control pill and she's also taking thyroid hormone replacement, it can affect her thyroid hormone dose requirements so she should have her thyroid hormone level tested.

"Outside pregnancy, some women take other forms of thyroid hormone, like triiodothyronine (T3) and desiccated thyroid, but those should not be used in pregnancy because they do not cross the placenta to supply needed thyroid hormone to the fetus."

HC: Do other forms of contraception affect women who are taking thyroid medication?

Elizabeth Pearce, MD: No, this only applies to estrogen-containing medications.

HC: Are there any side effects to taking thyroid hormone during pregnancy?

Elizabeth Pearce, MD: The treatment for hypothyroidism is levothyroxine. No other treatments are recommended in pregnant women. Outside pregnancy, some women take other forms of thyroid hormone, like triiodothyronine (T3) and desiccated thyroid, but those should not be used in pregnancy because they do not cross the placenta to supply needed thyroid hormone to the fetus.

There are no side effects of levothyroxine if the dose is correct, and it does not pose any risk to the baby or the pregnancy. As noted already, it's important for a woman to know that the dose needs to be increased as soon as she's pregnant.

HC: After birth, what should women do to take care of their thyroid?

Elizabeth Pearce, MD: If a hypothyroid woman is taking thyroid hormone during pregnancy and if her dose has been increased appropriately while she is pregnant she can typically go back to her pre-pregnancy dose as soon as she delivers. It's important that she should have her blood tested about six or eight weeks after delivery to make sure that her thyroid hormone dose is still the correct one for her.

Within the first 6 months after delivery, women are at risk for the development of a condition called postpartum thyroiditis. This is an autoimmune condition in which there is inflammation of the thyroid, and pre-formed thyroid hormone leaks into the circulation and to cause mild hyperthyroidism (high thyroid hormone levels) for several weeks. Sometimes this is followed by a phase of hypothyroidism when pre-formed hormone has been exhausted but the thyroid has not healed enough to produce new hormone. In most women, this condition is self-limited and will resolve without treatment. However, women who experience new symptoms of either hyperthyroidism (such as palpitations, tremor, or feeling too hot most of the time) or hypothyroidism (fatigue, constipation, feeling too cold most of the time) in the first months after giving birth should consult a care provider.

Yumhee Park
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Yumhee Park

Yumhee Park is a former content producer for HealthCentral and helped bring important stories of health advocates to life as a member of the Live Bold, Live Now multimedia team.