Hyperthyroidism in pregnancy


An overactive thyroid is an increased activity of the thyroid gland, which increases the production of the hormones triiodothyronine (T3) and thyroxine (T4).

This leads to an increase in the size and volume of the thyroid gland. The hormones formed are essential for the human organism and, if the active levels are too high, they cause an accelerated metabolism with many resulting symptoms.

An overactive thyroid during pregnancy may have existed before due to Graves' disease, for example, or thyroid autonomy. If the hyperfunction has reappeared, it is called pregnancy-associated hyperthyroidism.

Causes of an overactive thyroid during pregnancy

An overactive thyroid during pregnancy can have different causes.

Often the hyperthyroidism already exists before pregnancy, mostly due to Graves' disease.

Thyroid autonomy or an inflamed thyroid can also be possible causes.

However, the overactive thyroid can also occur during pregnancy. This is most likely in the first trimester, i.e. the first trimester of pregnancy. Pregnancy-associated hyperthyroidism can be caused by a greatly increased level of hCG in the blood.

This hormone, which is formed in the placenta, is increased in every pregnancy, especially in the first trimester and especially in multiple pregnancies. However, even with extremely high values, it can be an expression of an underlying trophoblastic disease.

HCG has a stimulating effect on the thyroid gland and thus causes an increase in size and function, which leads to hyperfunction. Pregnancy-associated hyperthyroidism rarely becomes symptomatic. Usually the values ​​are increased, but have no disease value (subclinical hyperthyroidism) and only require regular follow-up checks.

In most cases, the hyperthyroidism is self-limiting as the HCG level drops again from the second half of pregnancy and does not require any medication.

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If there is a suspicion of an overactive thyroid gland during pregnancy or to monitor the progress of known hyperthyroidism, a detailed anamnesis is first made. The focus here is on thyroid-specific symptoms.

This is followed by a palpation of the thyroid gland.

Blood will also be drawn to check thyroid levels (TSH, fT3, fT4) and possible antibodies.

The hCG value, which can play a role in pregnancy-associated hyperthyroidism, can also be measured. In addition, an ultrasound of the neck is performed, which assesses the size and volume of the thyroid gland.

Accompanying symptoms of an overactive thyroid during pregnancy

Symptoms of persistent under-treated hyperthyroidism are the same as they were before pregnancy. In pregnancy-associated hyperthyroidism, the symptoms are often milder, as it is a mostly self-limiting form of hyperfunction.

In the case of subclinical hyperfunction, the hyperthyroidism can also be completely symptom-free. Possible symptoms include increased blood pressure and pulse due to an accelerated metabolism, weight loss despite a good appetite, and frequent diarrhea.

Heat intolerance and sweating are also common and characteristic symptoms. Poor concentration, sleep disorders, nervousness and increased irritability can also occur in the context of an overactive thyroid. It can lead to increased hair loss and brittle nails.

There are numerous other, rarer symptoms that can be an expression of hyperthyroidism. Not all of the symptoms mentioned have to occur in every patient; even a few of them make the doctor suspect a thyroid disease.

Read more on the topic: Symptoms of hyperthyroidism

Nausea caused by hyperthyroidism during pregnancy

Hyperthyroidism during pregnancy is often associated with nausea and vomiting, especially if these are pregnancy-associated and non-pre-existing forms of hyperthyroidism.

It can then be the symptom complex of 'Hyperemesis gravidarum act in the case of transient hyperthyroidism ‘(THHG), i.e. severe vomiting caused by pregnancy and temporary hyperthyroidism.

Furthermore, the increased level of the hormone hCG formed in the placenta has a stimulating effect on thyroid function and vomiting.

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Therapy of hyperthyroidism during pregnancy

During pregnancy, the need for thyroid hormones and therefore also the hormone levels are increased in many pregnant women.

However, if there is an overactive thyroid due to thyroid autonomy or Graves' disease, drug therapy must be used, as otherwise there is a risk of health consequences for mother and child.

These risks can be greatly reduced with proper therapy. It is important to use the correct dosage and to take the medication according to the schedule recommended by the doctor, as otherwise the metabolic situation reversed and the hypothyroidism in the fetus or the newborn may occur.

In most cases, pregnancy-associated hyperthyroidism does not require the use of medication. This so-called gestational hyperthyroidism usually disappears on its own during the second trimester of pregnancy. Only regular checks of the thyroid values ​​should be carried out.

Which topics can be used?

During the first trimester of pregnancy, the active ingredient propylthiouracil (PTU) is the drug of choice.

It is only used for a limited time as the risk of PTU-induced liver failure is increased with prolonged use.

Only in the second and third trimester can the active ingredients carbimazole or thiamazole, which are used as standard in normal hyperthyroidism, be used, as these involve an increased risk of malformations in early pregnancy.

With the drugs used, a thyroid hormone level in the upper reference range is generally aimed for.

Beta-blockers can be used in the hCG-dependent form of hyperfunction.

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What are the consequences of an overactive thyroid during pregnancy?

The effects of untreated hyperthyroidism begin before pregnancy.

Often the willingness to conceive is reduced and women who suffer from an overactive thyroid try to become pregnant for a long time in vain.

Therefore, women planning pregnancy should undergo appropriate therapy.

This is all the more important because if pregnancy occurs, it can go unnoticed, as with most women, for a period of two to three months or even longer.

However, an optimal supply of thyroid hormones is particularly important in the first few weeks of pregnancy in order to support proper development of the child and to keep health risks for mother and child small.

Another possible consequence of untreated hyperthyroidism can also occur after pregnancy and is directly related to this. The mother may develop so-called postpartum thyroiditis, i.e. an inflammation of the thyroid gland during the puerperium, which develops around 4-24 weeks after delivery.

This disease usually has two phases. After the initial worsening of the hyperthyroid metabolic situation, the thyroid hormones decrease with a subsequent (sometimes permanent) hypothyroidism. However, only hyper- or hypothyroidism can occur in the course of the inflammation.

The role of iodine

The need for iodine is increased in every pregnancy, even with an overactive thyroid.

This ensures the supply of thyroid hormones to the fetus.

The general recommendation was that a total of 250 micrograms of iodine should be consumed per day. Since in most cases this dose is not absorbed through diet alone, pregnant women should take iodine preparations at a dose of 150 micrograms daily.

There are combination preparations with folic acid, which is also essential for pregnancy.

If the iodine supply is inadequate during pregnancy, goiter can develop (goiter) and an increased risk of miscarriages and stillbirths. Adequate iodine intake is also important during breastfeeding, where iodine-containing food supplements should also be taken.

Otherwise, low-iodine milk can impair the development of the newborn.

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What is the risk of an overactive thyroid gland during pregnancy?

Symptomatic hyperthyroidism in pregnancy carries numerous risks.

The mother's risk of developing preeclampsia, a condition with high blood pressure, water retention and protein in the urine, increases.

This can lead to premature birth or stillbirth. The pregnant woman can also develop heart failure, in which the heart is no longer able to perform its pumping function.

In very rare cases, a so-called thyrotoxic crisis can occur. This is an acute and life-threatening metabolic imbalance in the mother with effects on the child.

The risk of complicated pregnancy processes is also increased. The placenta may detach, i.e. the premature detachment of the placenta, which can endanger the child's life. Generally speaking, malformation and miscarriage rates are increasing. In the case of non-symptomatic, i.e. subclinical, hyperfunction, the risks mentioned are not increased.

The probability of occurrence of the complications mentioned is then similar to that of pregnant women with thyroid health.

How dangerous is an overactive thyroid during pregnancy for the baby?

A balanced thyroid function in the mother is particularly important in the first few weeks of pregnancy for the child to develop properly.

If symptomatic hyperthyroidism is not properly treated, there is a risk of premature birth, abortion or death.

The probability that the child will be born with a reduced birth weight of less than 2500 grams is also increased.

In addition, newborns born to mothers with hyperthyroidism often have poorer Apgar scores at the first examination directly after birth.

The risk of preeclampsia in the mother increases and if this disease manifests it can lead to premature birth or life-threatening complications for mother and child. There is also an increased risk of thyroid dysfunction in children.

It can also lead to an overactive thyroid. The higher the thyroid levels in the mother, the greater the risk or if, as in Graves' disease, antibodies are the cause. On the other hand, with an overactive thyroid, which is over-treated with medication, the reverse can occur and cause an underactive thyroid in the newborn.

The dangers mentioned for the unborn child do not apply to pregnant women with non-symptomatic hyperfunction. There is a general risk of complications here.