Hyperthyroidism – or having an overactive thyroid gland – can pose special concerns during pregnancy. When the body delivers too much thyroid hormone, both the mother and the baby can suffer. Miscarriages, premature births, and intrauterine growth retardation can occur when the disorder goes undiagnosed or untreated. Pregnant women with hyperthyroidism can also develop high blood pressure, and are at greater risk of heart conditions.
Many doctors will advise a woman with hyperthyroidism to get a permanent treatment -- such as radioactive iodine (RAI) or surgery -- before even trying to get pregnant. In that case, a woman is actually considered hypothyroid during pregnancy, and should follow directions for women with hypothyroidism. Other doctors who are more familiar with antithyroid drugs may be willing to work with women who have drug-managed hyperthyroidism.
But generally, however, when the disease is treated properly, most mothers have healthy pregnancies and babies. The best way to ensure a positive outcome is to find a well-trained obstetrician and endocrinologist familiar with the issues that might occur in a hyperthyroid pregnancy, take the appropriate medication, and closely monitor your thyroid levels in a timely manner. Think of your successful pregnancy as a team effort between all your health care providers, and most importantly, you.
Hyperthyroidism that arises during pregnancy is not terribly common, occurring in an estimated 2 out of 1,000 pregnancies. Most cases of hyperthyroidism in pregnancy stem from Graves' disease.
My heart's racing a mile a minute, I'm nervous and jumpy, short of breath, and always hot. What's more, I can't eat anything without throwing up. Is my thyroid out of control, or is this just how pregnant women feel?
That's hard to say, since some of the symptoms of "normal" pregnancies, such as an increased heartbeat, feeling hot, nervousness, nausea, etc., can mirror those of hyperthyroidism. If you have not yet been diagnosed with hyperthyroidism, but are pregnant, your doctor will need to conduct Thyroid Stimulating Hormone (TSH), plus free thyroxine (Free T4) and free triiodothyronine (Free T3), and perhaps thyroid antibodies tests as well, to diagnose your condition.
In addition to these blood tests, your healthier provider might look at a number of other factors to arrive at a diagnosis of uncontrolled hyperthyroidism, or simple, unpleasant pregnancy symptoms that befall a majority of women.
However, if you have a very rapid heart rate - above 100 beats per minute - and are losing weight instead of gaining during pregnancy, this might indicate that your overactive thyroid.
Doctors can't always rely on typical diagnostic tests – such as the radioactive iodine uptake test, or nuclear scanning – because of harm to the baby. Therefore, your healthier provider needs to be well-versed in a number of methods to differentiate true hyperthyroidism from normal pregnancy symptoms.
Sometimes pregnant women experience what's called hyperemesis gravidarum, or excessive vomiting, nausea, and weight loss. Occasionally patients suffering from this extreme nausea have blood test results that suggest a hyperthyroid condition, so more testing is usually ordered.
I have Graves' disease, and just found out I'm pregnant. How will my disorder be treated during my pregnancy? Will anything change?
It depends on what medication you're currently taking to control your disease. Two medications are typically used for controlling hyperthyroidism in pregnancy: methimazole (Tapazole) and propylthiouracil (PTU). Usually PTU is the drug of choice, since it's considered safer during pregnancy and causes less risk of crossing the placenta or harming your baby's developing thyroid gland. Some antithyroid drugs are never used during pregnancy, like Tapazole, which can be associated with some birth defects. Radioactive iodine (RAI) treatment is not done during pregnancy, because it can harm the baby's thyroid gland.
You may be one of the lucky women whose Graves' disease actually improves – or even goes into complete remission - during pregnancy. However, the disease returns postpartum, and sometimes worsens.
Generally, if you are pregnant and on PTU, you'll be taking less medication than you need when you're not pregnant. Your healthier provider will need to monitor your pregnancy closely and order frequent tests of your TSH, Free T4 and Free T3, so you'll probably see the doctor more often than pregnant women without your condition.
As it turns out, I'm pregnant, developed hyperthyroidism, and have discovered that I'm allergic to my antithyroid drugs. My doctor is recommending surgery. Is this safe? When should I have the surgery?
If you can't, or won't take medication, or the thyroid-suppressing drugs aren't doing the trick, sometimes surgery is recommended. Generally doctors won't perform a thyroidectomy (removal of the thyroid gland) in the first trimester, because the miscarriage rate might be slightly higher, or the third trimester, because of the possibility of premature labor. But for the most part, thyroid surgery during pregnancy can be conducted safely, and a good outcome for mother and baby ensured in most cases.
I really want to nurse this baby. Can I still nurse while taking my medication?
This is a controversial question. Some doctors believe you can take PTU, others disagree, and warn against any antithyroid drugs during breastfeeding. Since PTU and other medications like it suppress thyroid hormones, the baby needs to be monitored closely by your pediatrician, to ensure he or she does not become hypothyroid. Untreated, babies with hypothyroidism can suffer mental and physical impairment.
For more in-depth information on antithyroid drugs during breastfeeding, see my article on
Breastfeeding and Thyroid Disease.
Even if I take all my medication, can my baby still have problems, either at birth or afterward?
Possibly, but not likely. The chance of your baby being born with hyperthyroidism is extremely low – less than 2%. In some cases, thyroid-stimulating antibodies (such as those found in people with Graves' disease) may work on the baby's thyroid, causing it to work overtime. If it does happen, it's usually temporary, and can be easily treated with appropriate drugs. Be sure to let the hospital staff and your pediatrician know that you're hyperthyroid, and that your baby needs the appropriate tests. Shortly before your due date, doctors can attempt to estimate the chance of the baby developing hyperthyroidism with a blood test that measures your level of antibodies. Still, though, not all infants whose mothers tested high for the antibodies will become hyperthyroid.
You asked if your baby might develop problems down the road. It's highly unlikely, but it can happen. Your baby might have a normal thyroid function at birth, because of the antithyroid drugs still circulating in the placenta and in your blood. However, 7 to 10 days later, after the drugs have worn off, the infant might test hyperthyroid.
Again, a team effort between you and your healthier providers – to see that all the necessary testing is done – is vital to ensure that your baby stays healthy.
Read the Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success
Researcher/writer Laura Horton contributed to this article.