Fertility and Pregnancy Challenges With Thyroid Disease

The possibility of a new diagnosis and issues with current management

Having thyroid disease can impact your fertility, as well as your treatment plan once you do get pregnant. Your thyroid is crucial during pregnancy because it regulates the production of the thyroid hormones triiodothyronine (T3) and thyroxine (T4), both of which play a vital role in the development of your baby’s brain and nervous system.

When you've been diagnosed with thyroid disease, you should be regularly monitored throughout your entire pregnancy. If you have symptoms of a thyroid condition but you haven't been diagnosed, it's important to let your doctor know so that you can be properly monitored and treated to keep both you and your baby healthy.

Potential Fertility Challenges

Good thyroid function is essential to a healthy reproductive system, as well as your ability to successfully conceive, flourish through pregnancy, and deliver a healthy baby. The American Thyroid Association (ATA) recommends that all women seeking treatment for infertility have their thyroid-stimulating hormone (TSH) levels checked to rule out or diagnose thyroid disease since it can contribute to fertility difficulties. TSH is the hormone produced by the pituitary gland that triggers the production of T3 and T4.

Here are some common challenges you can run into when your thyroid disease is undiagnosed, untreated, or insufficiently treated.

Fertility Challenge

  • Your risk of having what's known as an "anovulatory cycle," a menstrual cycle in which your body doesn't release an egg, is higher.

What Happens

  • Though you can still have menstrual periods during anovulatory cycles, you can't get pregnant since there's no egg released to be fertilized.

One way to identify anovulatory cycles is through an ovulation predictor kit, which measures a surge of the particular hormones that occurs around ovulation. You may also use a manual or electronic fertility monitoring method, including temperature charting, to identify signs that can indicate ovulation.

Thankfully, proper diagnosis and treatment of your thyroid condition can reduce your risk of anovulatory cycles. Keep in mind that if you're still having anovulatory cycles once your thyroid function is stable, there are other potential causes that you should explore with your doctor like breastfeeding, perimenopausal changes, adrenal dysfunction, anorexia, ovarian issues, and polycystic ovary syndrome (PCOS), among others.

Fertility Challenge

  • You're at greater risk of having defects in the luteal phase of your menstrual cycle.

What Happens

  • If your luteal phase is too short, a fertilized egg ends up getting expelled with menstrual blood before it has time to implant.

A short luteal phase can often be identified by charting your basal body temperature (BBT). In some cases, your doctor may test your follicle-stimulating hormone (FSH), luteinizing hormone (LH), and progesterone levels as well.

Pointing to luteal phase defects as the cause of infertility and miscarriage is somewhat controversial since diagnosing them is difficult. Because of this, sufficient evidence hasn't been found to definitively say that luteal phase defects cause fertility issues, though the research thus far shows that it's highly likely that they play a role.

Proper thyroid diagnosis and treatment may resolve luteal phase defects in some women, but in others, insufficient progesterone—which is needed to produce a healthy uterine lining—may be the culprit. In these cases, supplemental progesterone has helped some women go on to have a healthy pregnancy and baby.

Fertility Challenge

  • You have a higher risk of hyperprolactinemia—elevated levels of prolactin, the hormone responsible for promoting milk production.

What Happens

  • Hyperprolactinemia can have a number of effects on your fertility, including irregular ovulation and anovulatory cycles.

Your hypothalamus produces thyrotropin-releasing hormone (TRH), which in turn triggers your pituitary gland to produce TSH, stimulating your thyroid gland to produce more thyroid hormone. When your thyroid isn't functioning properly, high levels of TRH may be produced, which can then cause your pituitary gland to also release more prolactin.

In breastfeeding women, the higher levels of prolactin generated to stimulate milk production often also help prevent pregnancy, illustrating why fertility issues can occur when your prolactin levels are too high and you're trying to get pregnant.

Charting your menstrual cycle and fertility signs, along with getting a blood test measuring your prolactin level, can help your doctor diagnose hyperprolactinemia. If proper thyroid diagnosis and treatment doesn't resolve the prolactin issue, several medications like bromocriptine or cabergoline may be prescribed, which can help lower your prolactin levels and restore your cycles and ovulation to normal.

Fertility Challenge

  • Thyroid disease can lead to an earlier onset of perimenopause and menopause.

What Happens

  • Menopause may occur before you're 40 or in your early 40s, shortening your childbearing years and causing reduced fertility at a younger age.

Perimenopause, the timeframe prior to menopause when your hormonal levels decline, can last as long as 10 years. And in the United States, the average age of menopause, when you stop having your menstrual period altogether, is 51 years. That means when you have thyroid disease, it's plausible that you can start having symptoms when you're around 30.

If you're experiencing perimenopausal changes, a full fertility evaluation, including evaluation of ovarian reserve, FSH, LH, and other hormones, can be performed by your physician to assess your fertility status. Based on the findings, your doctor may make recommendations regarding whether you're a candidate for natural conception or if you need assisted reproduction.

Take Charge of Your Care

Don’t assume that your fertility doctor will be on top of your thyroid issues. Surprisingly, some fertility doctors and clinics don’t pay much attention to thyroid testing or the management of thyroid disease during preconception, assisted reproduction (ART), or early pregnancy. Choose a fertility doctor who is thyroid-savvy and develop a plan to ensure that your thyroid disease doesn't interfere with a healthy pregnancy.

Screening in Pregnancy

In general, universal thyroid screening in pregnant women isn't considered justifiable, according to the ATA's guidelines for managing thyroid disease in pregnancy. However, the ATA does recommend that pregnant women have their TSH level checked when they have any of the following risk factors:

  • A personal history of thyroid dysfunction
  • Current signs or symptoms of thyroid disease
  • A family history of thyroid disease
  • A goiter (swelling in the thyroid gland)
  • A positive test for elevated thyroid antibodies
  • A history of thyroid surgery or neck or head radiation
  • Type 1 diabetes
  • A history of infertility, miscarriage, or preterm delivery
  • Other autoimmune disorders that are often linked to autoimmune thyroid disease such as vitiligo, adrenal insufficiency, hypoparathyroidism, atrophic gastritis, pernicious anemia, systemic sclerosis, systemic lupus erythematosus, and Sjögren's syndrome
  • Morbid obesity, defined as a body mass index (BMI) of over 40
  • Age over 30 years
  • A history of treatment with Cordarone (amiodarone) for heart rhythm irregularities
  • A history of treatment with lithium
  • Recent exposure to iodine as a contrast agent in a medical test
  • Living in an area that's considered iodine-insufficient

Thyroid Hormone Changes

Thyroid hormones are crucial to a developing baby's neurological and brain development. Even in women without thyroid disease, pregnancy places stress on the thyroid, increasing production of the thyroid hormones T3 and T4 by almost 50 percent. The reason for this is that during the first trimester, your baby is still developing a thyroid gland that's capable of producing its own hormones, so he or she completely depends on your supply, which is delivered through the placenta.

After around 12 to 13 weeks, your baby's thyroid gland is developed and he or she will produce some thyroid hormone, as well as continue getting thyroid hormone from you via the placenta. When you're pregnant, the increased demand for thyroid hormones continues until your baby is born.

The additional thyroid hormone production often causes your thyroid gland to grow by about 10 percent, though this isn't usually noticeable. However, in some cases, your doctor can see or feel this swelling in your thyroid (goiter).

Because normal thyroid function is different during pregnancy, your TSH levels will likely change as you progress from the first to third trimester, which your doctor monitors with blood tests. Chief among them is the TSH test, which measures the level of thyroid stimulating hormone in your blood.

Ideally, thyroid disease should be diagnosed and properly treated prior to conception. And if you're being treated for hypothyroidism and planning to conceive, before you get pregnant, you and your doctor should have a plan to confirm your pregnancy as early as possible and to increase your dosage of thyroid hormone replacement as soon as your pregnancy is confirmed.

Issues During Pregnancy

Different types of thyroid conditions have different issues when it comes to managing them in pregnancy.

Hypothyroidism

When your thyroid can't keep up during pregnancy, your TSH level will go up in underactive thryoid conditions, indicating a hypothyroid (underactive) state. If it's left untreated or insufficiently treated, your hypothyroidism can cause miscarriage, stillbirth, preterm labor, and developmental and motor problems in your child. The ATA recommendation is that, before you get pregnant, your doctor should adjust your dosage of thyroid hormone replacement medication so that your TSH is below 2.5 mIU/L to lower your risk of elevated TSH in the first trimester.

You may actually need to increase your thyroid medication dosage by 40 percent to 50 percent during your pregnancy. In fact, the ATA says that 50 to 85 percent of hypothyroid pregnant women will need to increase their dose, and this is more likely if you've had radioactive iodine treatment or thyroid surgery.

Using Synthroid (levothyroxine) during pregnancy is safe for your baby since the drug mimics your thyroid's natural thyroxine (T4) hormone.

According to the ATA guidelines, thyroid hormone replacement increases should start at home as soon as you think you're pregnant (ask your doctor for instructions on this) and continue through to around weeks 16 to 20, after which your thyroid hormone levels will typically plateau until delivery.

You'll need thyroid tests every four weeks during the first half of pregnancy and then again between weeks 26 and 32 to make sure your TSH is at a good level. Following delivery, your medication doses will need to be reduced to pre-pregnancy levels with follow-up monitoring six weeks after the delivery date.

Hashimoto's Disease

Hashimoto's disease, also known as Hashimoto's thyroiditis, is an autoimmune disease that attacks and gradually destroys your thyroid. Hypothyroidism is a common outcome of Hashimoto's, so if you're hypothyroid, you'll need the same treatment plan mentioned above.

That said, additional attention should be made to keeping your TSH level under 2.5 mlU/L, especially if you have thyroid antibodies, which are often present in Hashimoto's disease. The higher your TSH level is, the more your risk of miscarriage increases. When you also have thyroid antibodies, research published in 2014 shows that the risk of miscarriage increases even more significantly if your TSH level gets above 2.5 mIU/L.

Hyperthyroidism

If you have lower-than-normal TSH levels while you're pregnant, this shows that your thyroid is overactive, so your doctor should test you to determine the cause of your hyperthyroidism. It could be a temporary case that's associated with hyperemesis gravidarum (a condition of pregnancy that causes severe morning sickness), Graves' disease (an autoimmune thyroid disorder that's the most common cause of hyperthyroidism), or a thyroid nodule.

During pregnancy, hyperthyroidism is most often caused by either Graves' disease or temporary gestational hyperthyroidism, so your doctor will need to differentiate between these two. This can be a bit tricky since you can't have a radioactive iodine uptake scan of your thyroid while you're pregnant because of the risk it poses to your baby. Your doctor will need to rely on your medical history, a physical exam, clinical signs and symptoms, and blood tests to determine the cause of your hyperthyroidism.

If you've been vomiting, have no prior history of thyroid disease, your hyperthyroid symptoms are generally mild, and there's no evidence of swelling in your thyroid or the bulging eyes that can accompany Graves' disease, your doctor will probably chalk your hyperthyroidism up to temporary gestational hyperthyroidism. A blood test to check for elevated levels of the pregnancy hormone human chorionic gonadotropin (hCG) may also confirm this diagnosis since extremely high hCG levels are often found with hyperemesis gravidarum and can cause temporary hyperthyroidism.

In cases that aren't as clear-cut, your total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3) and/or TSH receptor antibody (TRAb) levels may be checked, depending on what your doctor is looking for. These blood tests can usually narrow down the cause of your hyperthyroidism so that your doctor can treat it appropriately.

The Importance of Treatment

You should begin treatment right away when you're pregnant and you become hyperthyroid due to Graves’ disease or thyroid nodules. Leaving hyperthyroidism untreated can result in high blood pressure, thyroid storm, congestive heart failure, miscarriage, premature birth, low birth weight, or even stillbirth. For pregnant and non-pregnant patients, treatment typically begins with taking antithyroid medications.

In cases where you're already being treated with a low dose of antithyroid medication and your thyroid function is normal, your doctor may take you off your medication, at least during your first trimester when your baby is most susceptible. You'll need to be monitored closely, having your TSH and FT4 or TT4 checked every one to two weeks during the first trimester and every two to four weeks during the second and third trimesters, as long as your thyroid function remains normal.

Otherwise, if you've been newly diagnosed, you haven't been taking antithyroid medication for very long, or you're at a high risk of developing thyrotoxicosis (a condition that occurs from having too much thyroid hormone in your system), your dosage will likely be adjusted so that you're on the lowest possible dose of antithyroid medication while still keeping your free T4 at the top end of the normal range or just above it. This protects your baby from overexposure since these medications are more potent for him or her than they are for you.

The antithyroid drug of choice during the first 16 weeks of pregnancy is propylthiouracil (PTU) because methimazole (MMI) has a higher (though small) risk of causing birth defects in your baby.

If you're currently on MMI, your doctor will likely switch you to PTU. It's unclear which one is better after 16 weeks, so your doctor will likely make a judgment call if you still need antithyroid medication at this point.

In cases where you have an allergic or serious reaction to both types of antithyroid drugs, you require very high doses to control your hyperthyroidism, or your hyperthyroidism is uncontrolled despite treatment, a thyroidectomy (thyroid surgery) may be recommended. The best time for a thyroidectomy is during your second trimester when it's least likely to endanger your baby.

You should never have radioactive iodine (RAI) treatment if you are or might be pregnant because of the risks to your baby. And if you've had RAI, you should put pregnancy off for a minimum of six months after treatment.

Graves' Disease

Whether you have active Graves' disease or you had it in the past, your baby has a higher risk of developing hyperthyroidism or hypothyroidism, either in utero (fetal) or after birth (neonatal). The factors that can affect these risks include:

  • Poorly controlled hyperthyroidism throughout your pregnancy, which can cause transient central hypothyroidism in your baby
  • Being on high doses of antithyroid drugs, which can lead to fetal and neonatal hypothyroidism
  • Having high levels of TSH receptor antibodies (TRAb) in the second half of your pregnancy, which can cause fetal or neonatal hyperthyroidism

The ATA recommends testing TRAb levels in pregnant women in these scenarios:

  • You've had treatment with radioactive iodine or surgery for Graves' disease
  • You were taking antithyroid medication when you found out you were pregnant
  • You need to take antithyroid medication throughout your pregnancy, in which case your TRAb level will need to be checked periodically

When you have TRAb present, as 95 percent of patients with active hyperthyroidism from Graves' do, these antibodies can cross the placenta and affect your baby’s thyroid if your levels become too high. A TRAb value that's more than three times above the upper limit of normal is considered a marker for follow-up of your baby, ideally involving a doctor who specializes in maternal-fetal medicine.

During your first trimester, if your TRAb levels are elevated, your doctor will need to keep a close eye on them throughout your pregnancy so that your treatment can be tailored to best minimize risk to both you and your baby.

In cases where your TRAb level remains elevated and/or your hyperthyroidism isn't well-controlled, you may have multiple ultrasounds performed. These should look for evidence of thyroid dysfunction in your developing baby, like slow growth, fast heart rate, symptoms of congestive heart failure, and an enlarged thyroid.

If you're a new mother with Graves’ disease, your newborn should be evaluated for neonatal/congenital hyperthyroidism and hypothyroidism, which has serious implications for newborns. In fact, the ATA recommends that all newborns be screened for thyroid dysfunction two to five days after birth.

Thyroid Nodules

Thankfully, the vast majority of thyroid nodules aren't cancerous. The ATA advises pregnant women with thyroid nodules to have their TSH level measured and to get an ultrasound to determine the features of the nodule and monitor any growth.

If you have a family history of medullary thyroid carcinoma or multiple endocrine neoplasia (MEN) 2, your doctor may also look at your calcitonin level, though the jury is still out as far as how helpful this measurement really is.

You may also have a fine-needle aspiration (FNA) biopsy of the nodule(s), especially if your TSH level isn't lower than normal. In cases where you have a nodule and your TSH is below normal, your doctor may put the FNA off until after you have your baby, but since it's considered safe during pregnancy, you can have an FNA done anytime.

When your thyroid nodule(s) is causing hyperthyroidism, you may need treatment with antithyroid medications. This will run along the same lines as anyone else with hyperthyroidism: Your doctor will put you on the lowest possible dose to keep your FT4 or TT4 on the high end to somewhat above the normal range to minimize risks to your baby.

Thyroid Cancer

When cancerous thyroid nodules are discovered during the first or second trimester—particularly if related to papillary thyroid cancer, the most common type—your doctor will want to monitor the cancer closely using ultrasound to see how and if it grows. If there's a fair amount of growth before your 24th to 26th weeks of pregnancy, you may need to have surgery to remove it.

If the cancer remains stable or it's discovered during the second half of your pregnancy, your doctor will likely recommend waiting until after your baby is born to have surgery.

In the case of anaplastic or medullary thyroid cancer, the ATA recommends that immediate surgery is seriously considered.

With any type of thyroid cancer, your doctor will put you on thyroid hormone replacement medication, if you're not already taking it, and monitor you closely to keep your TSH within the same goal range as before you were pregnant.

The Need for Iodine

Dietary iodine is the key building block for your body’s production of thyroid hormone. As discussed earlier, when you're pregnant, your thyroid increases in size and starts making more thyroid hormones to meet the needs of both mother and baby. Research from 2009 shows that you also need 50 percent more iodine daily when you're pregnant in order to be able to increase thyroid hormone production.

Pregnant women should get around 250 mcg of iodine every day. While the majority of women of childbearing age in the United States are not iodine deficient, this is also the group that's the most likely to have a mild to moderate iodine deficiency.

Since it's difficult to pinpoint who might be at risk of iodine deficiency, the ATA, Endocrine Society, Teratology Society, and American Academy of Pediatrics all recommend that pregnant women take 150 mcg potassium iodide supplements daily. Ideally, this should start three months before conception and last through breastfeeding.

The exception: If you're taking levothyroxine for hypothyroidism, you don't need iodine supplements.

Inexplicably, a large number of prescription and over-the-counter prenatal vitamins don't contain any iodine, so be sure to check labels carefully. In the ones that do, the iodine is usually from either kelp or potassium iodide. Since the amount of iodine in kelp can vary so much, choose supplements made with potassium iodide.

A Word From Verywell

While thyroid disease can affect your ability to get pregnant and your pregnancy itself, having a child can also give rise to postpartum thyroiditis. It's important that you continue to have your thyroid monitored closely after pregnancy to ensure that you are being properly managed.

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