Thyroid in Pregnancy: What You Need to Know

Updated January 22, 2020

After 3 miscarriages, Tara was finally able to maintain her pregnancy – only to go into labor 6 weeks early. Fortunately, her beautiful son, though premature, was healthy and didn’t need any special medical care. It was scary at first, and then got really stressful when she couldn’t, even with help from several lactation consultants, produce enough breastmilk for little Micah, who had to be given formula. She became depressed and felt like a total failure. Then she started gaining weight, rather than losing her ‘baby weight’ as she’d expected would happen. Even when Micah came home from the hospital, growing well, cooing, and happy, her depression just wouldn’t lift. Finally, at 6 months postpartum, she received a diagnosis: she had Hashimoto’s thyroiditis. Her thyroid labs had not been checked at all when she’d had the miscarriages, had not been trended during pregnancy, nor were they checked when her breastmilk production was low or to see if there was a medical reason for her depression – when she’d never struggled with depression before. While hindsight is 20/20, there’s a very good chance that many of Tara’s medical challenges – which caused her immense personal suffering – could have been prevented if these labs had been checked long ago, and her thyroid health properly cared for.

Healthy thyroid function is essential to the physical and emotional health of pregnant women and to new moms. It’s also critical for the health of the baby.

But thyroid problems often go undiagnosed during pregnancy. Studies show that when thyroid screening is done only on pregnant women who are at high risk for thyroid problems, an astonishing 55% of women with thyroid abnormalities are missed. And many of the common symptoms of hypothyroidism (when the thyroid is sluggish and underperforming) are attributed to the pregnancy itself. Those symptoms include fatigue, weight gain, GI distress, feeling depressed or anxious, and trouble sleeping. And, indeed, if you’re pregnant (even if you have the healthiest thyroid in the world) and you haven’t experienced some of those symptoms, you’re in the minority (and very lucky!) It’s easy to see how thyroid symptoms get missed during pregnancy.

Full disclosure: Thyroid problems tend to go unnoticed in non-pregnant women, too. Hypothyroidism, which predominantly affects women, is famously underdiagnosed. In fact, thyroid disease is so common among women, and so often neglected by conventional medicine, that I consider thyroid disease a feminist issue.

This is Your Thyroid During Pregnancy

During pregnancy, the body’s hormones shift as a natural response to supporting another life. Most pregnant women feel these rising hormonal tides in their day-to-day life: morning sickness, maybe some heartburn, increased appetite – all thanks to higher levels of key pregnancy-related hormones, like estrogen, progesterone, and human chorionic gonadotropin, or HCG, which is the hormone measured in blood or urine when you take a pregnancy test.

Thyroid hormone production shifts during pregnancy, too. The thyroid will produce more T4-binding globulin (TBG), which results in higher concentrations of the thyroid hormones T4 and T3 than in nonpregnant women. This helps to meet the body’s increased metabolic needs during pregnancy. (T4 and T3 are the primary hormones produced by the thyroid; if thyroid hormones are new to you and you want to learn more, click here.)

In other words, pregnancy puts increased demands on the thyroid – and that puts women who have pre-existing thyroid conditions, women who’ve had thyroid problems in previous pregnancies, and women who have subclinical hypothyroidism or nascent Hashimoto’s, at increased risk for thyroid problems during pregnancy.

The Risks of Thyroid Problems in Pregnancy

Thyroid problems in pregnancy can show up in several ways, the most common being hypothyroidism, either non-autoimmune, or autoimmune – also called Hashimoto’s.

Hypothyroidism is characterized by high TSH and low free T4. Subclinical hypothyroidism is characterized by elevated TSH but normal free T4 and T3 – or by the presence of thyroid TPO antibodies when other thyroid numbers are within the optimal range.

Overt hypothyroidism presents a greater risk of causing problems (and often more severe problems) in pregnancy, but a subclinical status should not be ignored.

The risks of hypothyroidism during pregnancy include:

  • Increased rate of first-trimester miscarriage
  • Preeclampsia and gestational hypertension
  • Preterm delivery
  • Increased rate of cesarean section
  • Postpartum hemorrhage
  • Impaired neurological development in children (studies have linked hypothyroidism in pregnancy to autism spectrum disorders)

Some studies have shown similar risks in pregnant women with subclinical hypothyroidism.

Further, hypothyroidism during pregnancy can be a harbinger of thyroid problems after pregnancy: the risk of developing postpartum thyroiditis increases by 40 to 60 percent if you test positive in the first or early-second trimester. And thyroid problems postpartum lead to even more fatigue than the typical exhaustion associated with being a new mom. Postpartum thyroiditis can also bring depression, hair loss, difficulty losing weight, and trouble producing adequate breast milk.



This is one of the reasons I strongly recommend simple thyroid testing early in pregnancy for all women, despite the recommendations by some professional medical organizations to only test pregnant women who are at high risk. And, if those test results show signs of thyroid problems or nascent thyroid problems, continue to get tested at regular intervals during pregnancy. Knowing about – and treating – thyroid issues early on can help prevent health risks to mother and baby during pregnancy, including one of the most heartbreaking problems associated with hypothyroidism in pregnancy: miscarriage.

Before You Conceive

Not only can thyroid problems add to postpartum exhaustion, depression, and stubborn weight loss resistance, they can also make it harder to get pregnant. Optimally, women who are trying to conceive should have their thyroid function checked and, if their labs aren’t optimal, should seek support and treatment. Women undergoing in vitro fertilization may also benefit from knowing and optimizing their thyroid numbers during the IVF process. (I’ll be writing more about thyroid health when trying to conceive in a future blog post.)

 Hypothyroid, Hashimoto’s, and Miscarriage Risk

Miscarriage, although much more common than most women realize, is so often an incredibly painful experience emotionally and psychologically, and women suffer silently and all too alone. Women are generally told that ‘it just happens’ or ‘it’s for the best because there were probably chromosomal problems.’ While sometimes we just don’t know why miscarriage happens, and chromosomal problems do cause miscarriage, so can hypothyroidism – and this is a ‘fixable’ problem.

Women who test positive for TPO antibodies are at the highest risk for adverse pregnancy outcomes and miscarriage. What’s more, research suggests that these adverse outcomes occur at a lower TSH than in women without TPO antibodies. That’s why TPO antibody testing in pregnancy is SO critical – and why even if you only test positive for TPO antibodies (and all your other numbers are in range) it’s important to seek treatment.

What’s more, women who already take supplemental thyroid hormone may not be sufficiently covered by their current dose during pregnancy. Because the need for thyroid hormone in the body goes up during pregnancy, many women already taking medication may need to increase their thyroid hormone doses during the first trimester. Studies suggest that between 24 and 55 percent of women who are already on levothyroxine (a supplemental thyroid hormone medication also known as Synthroid) have elevated TSH at their first prenatal doctor’s visit.



Most labs have trimester-specific reference ranges for thyroid numbers. One large population-based study found that antibody-negative pregnant women with TSH values in the optimal range (under 2.5 mU/L) during the first trimester miscarried significantly less than antibody-negative women with TSH values between 2.5 and 5.0 in early pregnancy. Levothyroxine can be used during early gestation to help lower TSH numbers.

Low FT3 or FT4 suggest the need for further testing and possible medication to supplement thyroid hormone. Elevated anti-TPO antibodies alone in pregnancy does not suggest the need for thyroid hormone treatment, however, the supplements recommended below in this article are important for reducing these antibodies. Elevated antibodies indicate a much higher risk for progression to overt Hashimoto’s during the pregnancy, after baby is born, or later in life. Normalizing them can protect against this.

If you’re taking supplemental thyroid hormone for the first time during pregnancy, I recommend levothyroxine. Most OB’s are familiar with levothyroxine and will know how to dose and manage it for you. Many OBs are less familiar with other drugs, and because proper dosing is SO important during pregnancy, I recommend switching to a different medication only if levothyroxine doesn’t improve your lab values.

Research suggests that pregnant women who have tested positive for TPO antibodies, and who are taking levothyroxine (even when treatment duration is short), reduce the chances of pregnancy loss.

Thyroid Function and Baby’s Well-Being

Suboptimal maternal thyroid function has the potential to impact the baby’s eventual growth and development. Studies have shown that maternal hypothyroidism in early gestation is associated with poor cognitive function, poor psychomotor development, and low IQ in children. Newer research has connected maternal hypothyroidism with emotional and behavior problems in offspring. Children are also more likely to eventually experience their own thyroid problems.

Studies have linked severe hypothyroidism in early pregnancy (sometimes called maternal hypothyroxinemia) with increased risk for autism in babies. The risk for women with severe hypothyroidism of having a baby who is diagnosed with autism is 4-times greater than it is for women with optimal thyroid function. These findings add more proof to the value of testing thyroid labs early in pregnancy.

Thyroid Medication in Pregnancy – Is it Necessary?

If TSH is elevated or FT3 or FT4 are low, then taking thyroid medication is necessary. If you already have a known diagnosis of Hashimoto’s and are on medication, medication levels should automatically be adjusted with an increase of up to 50% to compensate for the additional demands of pregnancy on your metabolism and thus your thyroid. This should be done with the guidance of your midwife or doctor, and follow-up labs should be done to make sure you are at the best dose for your new prenatal needs.

To Reverse Elevated Thyroid Auto-Antibodies

Take Selenium: Selenium has been shown to reduce TPO antibodies and slow or stop the development of Hashimoto’s. Selenium is safe for pregnant women and I recommend taking up to 200 mcg/day (do not exceed that amount) during pregnancy and for up to six months after giving birth. Selenium can also be obtained from food, particularly Brazil nuts – though I recommend eating selenium-rich foods in conjunction with a supplement, not as a replacement. Just one or two Brazil nuts a day can help boost the body’s selenium stores. I also recommend other selenium-rich foods like mushrooms, chicken, eggs, lamb, cod, turkey, and halibut.

Research also suggests that taking selenium together with myo-inositol has a remarkably powerful effect on restoring TSH levels to a healthy range, reducing both TPOAb and TgAB antibodies, and enhancing thyroid hormone production. The dose is 200 mcg/day of selenium and 600 mg/day of myoinositol.

Vitamin D: Studies show that vitamin D levels tend to be lower in people with hypothyroidism. Because the body needs vitamin D to produce and use thyroid hormones, and because vitamin D is an important immune modulator that’s involved in hundreds of health-sustaining functions in the body – including bone health, mood, blood sugar regulation, and energy – it’s important to have optimal levels during pregnancy (and when not pregnant, too, for that matter!). In some cases, vitamin D is the missing link when a woman is already on supplemental thyroid hormones, but her dose needs keep changing or she’s not seeing results. Low vitamin D can be the culprit hiding in the background. Get your D tested and supplement with 2000-4000 units daily if your levels are low. Optimal blood level is between 50 and 80.

Test and Retest

If there’s one thing I hope you take away from this post, it’s the importance of testing early in pregnancy, if you’re trying to conceive, or if you’ve had a history of miscarriage or postpartum depression, and optimizing your thyroid lab numbers. The adverse outcomes associated with suboptimal thyroid function in pregnancy are real – and can be devastating – and are also preventible and reversible.

Get to the Root Causes

Here’s the good news: thyroid problems can be fixed, often with natural and lifestyle interventions. Yes, in some cases, both pregnant and nonpregnant women require supplemental thyroid hormones – and that’s not to be interpreted as a failure of lifestyle interventions – but all women with thyroid problems (whether they take thyroid medication or not) can work to heal Root Causes with natural strategies.

For more on the Root Causes of poor thyroid function and how to heal them, check out my book The Adrenal Thyroid Revolution. The strategies in the book can be especially important during pregnancy, when the thyroid is doing its work for two, and the book provides clear indications as to which supplements are – and aren’t appropriate – in pregnancy and while breastfeeding.

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Great post. Very important information. Thank you!

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Thank you for this info. I recently had a miscarriage and had signs of hypothyroidism. I am currently 5 weeks pregnant again and this time will demand that they test me and continue to check to avoid any problems.