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What is hyperthyroidism during pregnancy?

Changes in thyroid function are related to pregnancy in multiple ways. While thyroid abnormalities can affect pregnant women, pregnancy itself can trigger changes in thyroid function, and problems with thyroid hormones can reduce your fertility, making it hard to get pregnant in the first place. Hyperthyroidism is the state in which your thyroid is overactive, meaning that it is making and releasing too much of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4), thus, accelerating your metabolism and producing a range of symptoms and other effects throughout your body, including fertility difficulties. Once you are pregnant, you can become hyperthyroid, as well.

With hormone levels, there is a kind of Goldilocks zone, an optimal range of concentrations in the blood that supports health. Like the bowls of porridge in the Goldilocks story being too hot or too cold, with the thyroid, too little, meaning hypothyroidism, causes problems, whereas too much, hyperthyroidism causes a different set of problems. As your body shifts into pregnancy mode, your physiological needs shift so that the just right range of thyroid hormones is slightly higher than for non-pregnant women. Normally, this need is met, because levels of the pregnancy hormone, beta-human chorionic gonadotropin (ß-hCG), rise rapidly until peaking near the end of the first trimester. The signal for the thyroid to increase the production of thyroid hormone comes from another hormone, called thyroid-stimulating hormone (TSH), produced by the pituitary gland in the brain. As when youre not pregnant, TSH continues to work as a messenger to the thyroid during pregnancy, but the chemical structure of ß-hCG is similar to TSH, enough so that ß-hCG also stimulates the thyroid to produce its hormones. This means that by the end of the first trimester, it is normal to be hyperthyroid, so long as youre not too hyperthyroid, meaning out of the Goldilocks zone, where symptoms of hyperthyroidism become problematic. However, in addition to normal hyperthyroidism due to ß-hCG, there are other things that cause hyperthyroidism, the main one being an autoimmune condition called Graves disease hyperthyroidism caused by antibodies that your immune system produces and that stimulate the thyroid gland. Less common causes of hyperthyroidism include certain pituitary tumors that produce excessive amounts of TSH and tumors in the thyroid itself that produce thyroid hormones (thyroid adenoma).

Finally, after you deliver, during the post-partum period, there is a phenomenon, called post-partum thyroiditis, which is similar to another autoimmune condition called Hashimoto thyroiditis which usually causes hypothyroidism (the opposite of hyperthyroidism), but first causes a brief period (usually a couple of weeks) of hyperthyroidism, due to thyroid cells getting damaged and releasing their hormones into the blood.

How common is hyperthyroidism during pregnancy?

Hyperthyroidism, beyond the normal increase in thyroid hormones during pregnancy, has been reported to occur in approximately 2 per 1,000 pregnancies (0.2 percent), usually due to Graves disease. It is possible that many cases of hyperthyroidism are not reported since symptoms of mild to moderate hyperthyroidism can be mistaken for normal pregnancy phenomena if they are not investigated.

How is hyperthyroidism during pregnancy diagnosed?

Symptoms of hyperthyroidism, such as palpitations, nervousness, increased appetite, eye discomfort, gastrointestinal disturbances, feeling that you are hot, fatigue or muscle weakness, and difficulty sleeping can serve as an initial hint that you are hyperthyroid. Some of these symptoms can overlap with those of normal pregnancy, but certain findings on the physical examination, such as protruding eyeballs, an enlarged or tender thyroid (goiter), rapid or irregular heartbeat, and weight loss or not enough weight gain for your stage of pregnancy, can be hints as well that your thyroid is overactive. Normally, you should gain 1-2 kilograms (2 -5 pounds) during the first trimester, and after that, about 0.5 kg (1 lb) per week, but hyperthyroidism tends to decrease this weight gain.

For a definitive diagnosis, you will supply a blood sample to be tested for levels of TSH and thyroid hormone, specifically free T4, meaning T4 hormone that is not bound to a special protein called Thyroid-binding globulin (TBG). In hyperthyroidism, your T4 level is too high, and, if the pituitary is not the underlying problem, then your TSH level is too low. If your TSH level is just a little bit below normal, this may be consistent with the normal hyperthyroidism of pregnancy, caused by ß-hCG. Women with a multiple pregnancy (twins, triplets, or higher) are more likely to be more into the hyperthyroid range since ß-hCG levels are higher than in singleton pregnancies. If TSH is far too low, and thyroid hormones are too high in your blood, then its much more likely that your hyperthyroidism is Graves disease. To find out if Graves disease is the diagnosis, your blood will be tested for antithyroid antibodies, which, if present, would enable the diagnosis. In the unlikely event of a pituitary cause of your hyperthyroidism, your TSH level would be too high, rather than too low, despite your thyroid hormones being high, in which case you would need imaging tests, such as magnetic resonance imaging (MRI) of the head.

If you are experiencing symptoms of hyperthyroidism after delivery, this could be Graves disease, but it also could be post-partum hyperthyroidism due to the Hashimoto-like immune system condition that stimulates the thyroid initially, but then causes hypothyroidism – there are blood tests for this, too.

Does hyperthyroidism cause problems during pregnancy?

As noted earlier, hyperthyroidism essentially accelerates your metabolism, causing a range of symptoms, such as heart palpitations, nervousness, increased appetite, eye discomfort, gastrointestinal disturbances, feeling that you are hot (although this is very subjective and not always the best indicator for hyperthyroidism), fatigue or muscle weakness, and difficulty sleeping. Weight loss during pregnancy, or a failure to gain enough weight, is a profound effect of hyperthyroidism. Your heart also is at risk if the hyperthyroidism is severe, because the excess thyroid hormones stimulate the heart to beat too fast, which strains your heart and can lead to arrhythmias (fast and/or irregular heartbeats) and can also cause clotting of blood. All of this potentially could lead to acute coronary syndrome (heart attack) and even heart failure in severe cases. Having hyperthyroidism while pregnant also means that you have an elevated risk for a couple of complications, particular to pregnancy. One such pregnancy complication is hyperemesis gravidarum (HG), a severe form of pregnancy nausea and vomiting, which also is related to increases in ß-hCG levels. The other complication is preeclampsia, featuring high blood pressure and dysfunction of an internal organ, usually the kidney. If you suffer post-partum thyroiditis, the hypothyroidism generally will not be as severe as the hypothyroidism of Graves disease, and it will resolve, usually within a couple of weeks.

Does hyperthyroidism cause problems for the baby?< /p>

Since hyperthyroidism interferes with your weight gain during pregnancy, the fetus is at risk of low-birth-weight, plus there is an elevated risk of spontaneous abortion (miscarriage), preterm labor, and stillbirth. During the first trimester, the embryo/fetus does not make its own thyroid hormones, but the maternal thyroid hormones cross the placenta in very small quantities, enough to meet the babys needs. On the other hand, thyroid-stimulating antibodies of Graves disease cross the placenta fairly easily, and this can happen throughout pregnancy. Thus, once the fetus can make its own thyroid hormones (during the second trimester), stimulation by the antibodies can cause excessive production of fetal thyroid hormones. This leads to whats called fetal thyrotoxicosis, and, when born, the baby can have neonatal thyrotoxicosis. This means toxicity from excessive amounts of the hormones T3 and T4, which has dangerous consequences for various organ systems, just as it does in adults.

What to consider about taking medications when you are pregnant or breastfeeding:

  • The risks to yourself and your baby if you do not treat the hyperthyroidism
  • The risks and benefits of each medication you use when you are pregnant
  • The risks and benefits of each medication you use when you are breastfeeding

What should I know about using medication to treat hyperthyroidism during pregnancy?

If the hyperthyroidism is due solely to elevated levels of ß-hCG, the condition usually will subside as you enter the second trimester, when ß-hCG levels are dropping, or soon after, so no treatment is needed for the hyperthyroidism itself. However, medications are often appropriate to treat symptoms, such as excessive stimulation of the heartbeat, and in all cases, when you have Graves disease. To slow your heart rate, doctors may prescribe a beta-blocker medication. In non-pregnant people with hyperthyroidism due to Graves disease, an adenoma (a benign tumor that makes thyroid hormones), or some other condition that does not resolve, the main treatment consists of iodine-131, a radioactive isotope. It gets absorbed by the thyroid gland, which it destroys because it emits gamma-rays. This works because iodine-131 is quite a strong gamma-ray emitter, so strong that somebody sleeping next to you night after night actually gets a fairly high radiation exposure.

Consequently, the treatment is contraindicated in pregnant women since the radiation can be harmful to the fetus. Some medications can reduce thyroid activity, the main ones being: propylthiouracil (PTU) and methimazole. Of these two, methimazole is contraindicated during early pregnancy because it can cause birth defects. PTU is the treatment of choice for pregnant women, although it can produce rare, but severe, complications, including aplastic anemia, a potentially life-threatening condition, and also severe liver problems. Consequently, some doctors prefer to change the medication from PTU to methimazole during the latter part of pregnancy, when it is not thought to produce birth defects. In determining the dosage of your medication, doctors will titrate the drug, meaning that they will tweak the dosing and timing of when you take the drug based on the levels of TSH in your blood. Generally, the goal will be to reduce your thyroid hormone levels enough to make you feel better by eliminating, or dramatically reducing, your symptoms, but leaving you a little bit hyperthyroid, rather than bringing your thyroid activity to normal non-pregnancy levels, since doing that can cause some problems for the baby.

Who should NOT stop taking medication for hyperthyroidism during pregnancy?

You should discuss any desire to change your anti-thyroid medication regimen with your doctor, since getting dosing and desired effects just right is fairly difficult. As for medications to treat symptoms, such as beta-blockers to slow your heart, you should never stop taking such medications abruptly, but rather discuss any concerns with your doctor.

What should I know about choosing a medication for my hyperthyroidism during pregnancy?

It is important to stay in communication with your health care provider as the release of new studies over time can change the outlook on the role of specific medications during pregnancy.

You may find Pregistrys expert reports about the medications to treat this condition here. Additional information can also be found in the sources listed below.

What should I know about taking a medication for my hyperthyroidism when I am breastfeeding?

Some controversy surrounds the question of which anti-thyroid medication is safest for nursing mothers. Some research suggests that methimazole might be a safer choice than PTU during breastfeeding.

What alternative therapies besides medications can I use to treat my hyperthyroidism during pregnancy?

For those with hyperthyroidism that does not resolve with medications, there is an option for thyroidectomy, surgical removal of the thyroid gland. Outside of pregnancy, this is the most extreme treatment. During pregnancy, however, if anti-thyroid medications are not adequate since you cannot be given iodine-131, surgery actually would be the next option. If your thyroid does need to be removed, you would then need to take thyroid hormones on a long-term basis.

What can I do for myself and my baby when I have hyperthyroidism during pregnancy?

It is very important to follow the instructions of your physician.

Resources for hyperthyroidism in pregnancy:

For more information about hyperthyroidism during and after pregnancy, contact http://www.womenshealth.gov/ (800-994-9662 [TDD: 888-220-5446]) or contact the following organizations:

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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

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