Fertility and Pregnancy Challenges With Thyroid Disease

The possibility of a new diagnosis and issues with current management


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.


Fertility Challenge


What Happens



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


What Happens


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.


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


What Happens




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


What Happens



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


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
  • Age over 30 years
  • A history of treatment with lithium
  • 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



When your thyroid can't keep up during pregnancy, your TSH level will drop, 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.


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.


Hashimoto's Disease




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.


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





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.



Graves' Disease



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


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.



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.


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 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.



A Word From Verywell


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