OVERVIEW

What is gestational hyperthyroidism syndrome?

Gestational hyperthyroidism syndrome, also known as transient hyperthyroidism of hyperemesis gravidarum (THHG), is a temporary pregnancy-related hyperthyroidism. It typically occurs between 8–10 weeks of gestation and resolves by 14–18 weeks.

This condition is associated with elevated levels of human chorionic gonadotropin (HCG) in the blood during early pregnancy.

Gestational hyperthyroidism syndrome may cause symptoms such as heat intolerance, excessive sweating, mood swings, vomiting, and palpitations. Blood tests for thyroid function often show decreased or undetectable thyroid-stimulating hormone (TSH) levels, along with elevated free thyroxine (FT4) and total thyroxine (TT4) levels.

Currently, it is believed that this condition generally does not affect fetal growth, development, or intellectual development. Treatment mainly focuses on symptomatic and supportive care, such as managing severe vomiting and correcting dehydration with fluid replacement. Oral antithyroid medications are usually unnecessary.

Is gestational hyperthyroidism syndrome common?

Gestational hyperthyroidism syndrome is a common thyroid dysfunction in early pregnancy, occurring in approximately 2–3 out of every 100 pregnant women.

SYMPTOMS

What are the common symptoms and manifestations of gestational hyperthyroidism syndrome?

The manifestations of gestational hyperthyroidism syndrome are not very obvious and may include:

• Heat intolerance, excessive sweating, emotional instability, vomiting, palpitations, and increased heart rate at rest (heart rate exceeding 100 beats per minute);

• Increased appetite, with no weight gain in the pregnant woman despite increased food intake as pregnancy progresses;

• Increased pulse pressure during blood pressure measurement, where the difference between systolic (high) and diastolic (low) pressure exceeds 50 mmHg;

• Additionally, most pregnant women with gestational hyperthyroidism syndrome often experience pronounced pregnancy symptoms, accompanied by hyperemesis gravidarum (severe vomiting).

What are the risks of gestational hyperthyroidism syndrome? Is this condition serious?

Gestational hyperthyroidism syndrome is a temporary form of hyperthyroidism. As pregnancy progresses, the symptoms of hyperthyroidism gradually alleviate, and thyroid hormone levels return to normal.

With close monitoring of the pregnant woman's symptoms, regular follow-ups (e.g., every 2–4 weeks) to track thyroid hormone changes, and symptomatic treatment (including antiemetics, energy balance, correction of water-electrolyte imbalances, and heart rate control), gestational hyperthyroidism syndrome generally does not adversely affect the pregnancy.

CAUSES

What causes gestational hyperthyroidism syndrome?

After pregnancy, the placenta secretes human chorionic gonadotropin (HCG), the hormone detected in pregnancy tests. A significant increase in HCG indicates pregnancy and is also the cause of pregnancy-related symptoms, such as morning sickness.

HCG has a very similar structure to thyroid-stimulating hormone (TSH). Therefore, elevated HCG can "overstep its bounds" and act like TSH, stimulating the thyroid to secrete thyroid hormones. This leads to a significant increase in thyroid hormone levels (such as free thyroxine FT4) in expectant mothers, resulting in a series of discomfort symptoms.

Since HCG "takes over" the role of TSH, TSH becomes "redundant," leading to a noticeable decrease in TSH levels in the body.

Who is more likely to develop gestational hyperthyroidism syndrome?

Gestational hyperthyroidism syndrome is related to pregnancy and only occurs in expectant mothers. Conditions such as hyperemesis gravidarum, multiple pregnancies, placental hypertrophy, ovarian luteinizing cysts, hydatidiform mole, or choriocarcinoma can lead to high HCG levels, increasing the likelihood of gestational hyperthyroidism syndrome.

Is gestational hyperthyroidism syndrome contagious?

No.

Is gestational hyperthyroidism syndrome hereditary?

No.

DIAGNOSIS

What are the diagnostic criteria for gestational hyperthyroidism syndrome?

Doctors primarily rely on the characteristics of the pregnant woman, blood tests, and ultrasound examinations to diagnose gestational hyperthyroidism syndrome. The diagnosis generally requires several key features:

• It occurs in the first trimester and usually resolves by weeks 14–18 of pregnancy.

• Blood tests show significantly elevated levels of human chorionic gonadotropin (HCG).

• Symptoms may include heat intolerance, excessive sweating, emotional instability, palpitations, a resting heart rate exceeding 100 beats per minute, increased appetite, failure of maternal weight to increase with gestational age, and widened pulse pressure.

• No personal or family history of autoimmune thyroid disease.

• Blood tests reveal elevated thyroid hormone levels (e.g., free thyroxine FT4, total thyroxine TT4) and decreased thyroid-stimulating hormone (TSH). Thyroid-related antibodies (thyroid peroxidase antibody TPOAb, thyrotropin receptor antibody TRAb) are typically negative.

• Thyroid ultrasound shows no signs of hyperthyroidism, including no significant increase in thyroid blood flow or peak systolic velocity of the thyroid artery.

What tests are needed for gestational hyperthyroidism syndrome?

Generally, blood tests and ultrasound examinations are required.

• Blood tests include:

• Thyroid function and thyroid antibody tests: To assess thyroid function.
  Typical results show elevated thyroid hormone levels, particularly free thyroxine (FT4) and total thyroxine (TT4), with decreased or undetectable thyroid-stimulating hormone (TSH). Thyroid-related antibodies (thyroid peroxidase antibody TPOAb, thyroglobulin antibody TgAb, thyrotropin receptor antibody TRAb) are usually negative.

• Electrolyte tests: To check for electrolyte imbalances, especially in cases of hyperemesis gravidarum, as about 60% of gestational hyperthyroidism syndrome cases involve electrolyte abnormalities.

• Liver function tests: To evaluate liver function, as about 50% of gestational hyperthyroidism syndrome cases show liver function abnormalities.

• Ultrasound examinations include:

• Thyroid ultrasound: Mainly to rule out hyperthyroidism during pregnancy by assessing thyroid blood flow and peak systolic velocity of the thyroid artery.

• Pelvic ultrasound: To evaluate for multiple pregnancies or molar pregnancies.

Are gestational hyperthyroidism syndrome and hyperthyroidism during pregnancy the same condition?

Gestational hyperthyroidism syndrome and hyperthyroidism during pregnancy are completely different conditions.

• Gestational hyperthyroidism syndrome

• Occurs in the first half of pregnancy, is short-lived, and is related to increased HCG production. It affects 30%–60% of pregnant women with hyperemesis gravidarum.

• Thyroid function tests mainly show elevated free thyroxine (FT4) and total thyroxine (TT4), while thyroid-related antibodies (thyroid peroxidase antibody, thyroglobulin antibody, thyrotropin receptor antibody) are typically negative.

• This condition tends to resolve as pregnancy progresses and usually does not require antithyroid medication.

• Hyperthyroidism during pregnancy

• Can occur at any stage of pregnancy, often without significant nausea or vomiting, and is rarely associated with hyperemesis gravidarum. However, eye symptoms (e.g., exophthalmos) are often more pronounced.

• Thyroid function tests mainly show elevated free triiodothyronine (FT3) and total triiodothyronine (TT3), and thyroid-related antibodies (thyrotropin receptor antibody) are usually positive.

• This condition does not resolve on its own and requires treatment with antithyroid medications.

TREATMENT

Which department should I visit for gestational hyperthyroidism syndrome?

Generally, choose the endocrinology department, but you can also go to the obstetrics and gynecology department.

Can gestational hyperthyroidism syndrome resolve on its own?

Yes, gestational hyperthyroidism syndrome usually resolves by weeks 14–18 of pregnancy.

How is gestational hyperthyroidism syndrome treated?

Treatment primarily involves monitoring the condition, checking thyroid function every 2–4 weeks, and providing symptomatic relief as needed.

• For hyperemesis gravidarum, control vomiting, correct dehydration, and maintain energy and electrolyte balance.

• For rapid heart rate, control the heart rate. If tachycardia occurs, short-term use of β-adrenergic receptor blockers like propranolol (10 mg every 6–8 hours) may be considered. However, long-term use of β-blockers may lead to adverse outcomes like fetal growth restriction.

• Oral antithyroid drugs are not recommended for gestational hyperthyroidism syndrome. They are only considered when it is difficult to distinguish from pre-existing hyperthyroidism, with timely adjustments based on the condition.

Is hospitalization required for gestational hyperthyroidism syndrome?

Hospitalization is generally unnecessary. However, pregnant women with severe hyperemesis, dehydration, or electrolyte imbalances may require hospitalization for fluid therapy, vomiting control, and electrolyte balance restoration.

Under what circumstances might oral antithyroid drugs be used for gestational hyperthyroidism syndrome?

• Severe symptoms with extremely high thyroid hormone levels (e.g., FT4, FT3).

• Persistent vomiting despite symptomatic treatment for over a week.

• Hyperthyroidism symptoms persisting into the second trimester.

• Difficulty distinguishing gestational hyperthyroidism syndrome from pre-existing hyperthyroidism.

What are the common side effects of medications for gestational hyperthyroidism syndrome?

Common oral antithyroid drugs include methimazole and propylthiouracil:

• Methimazole may cause fetal malformations, such as skin aplasia and "methimazole-associated embryopathy," including choanal/esophageal atresia and facial deformities.

• Propylthiouracil may lead to liver damage or even acute liver failure. Under medical supervision, proper dosing can minimize these risks.

For tachycardia, short-term β-blockers like propranolol may be used. Short-term use is generally safe, but long-term use may cause fetal growth restriction.

Can gestational hyperthyroidism syndrome be completely cured?

Yes, gestational hyperthyroidism syndrome occurs only during pregnancy and resolves completely. It typically resolves on its own by weeks 14–18 of pregnancy.

DIET & LIFESTYLE

What should pregnant women with hyperthyroidism syndrome pay attention to in their diet?

Due to misunderstandings about iodized salt, many people believe that non-iodized salt is healthier, but this view is incorrect.

During pregnancy, it is particularly important to ensure adequate iodine intake to support the healthy development of both the mother and the baby. Therefore, iodized salt is recommended during pregnancy and breastfeeding.

What should pregnant women with hyperthyroidism syndrome pay attention to in daily life?

Hyperthyroidism syndrome during pregnancy leads to elevated thyroid hormone levels, putting the body in a hypermetabolic state. Therefore, it is important to avoid fatigue and strenuous exercise, prioritize rest, maintain a regular routine, and consume plenty of fruits and vegetables rich in vitamins.

Does hyperthyroidism syndrome during pregnancy require follow-up tests? How are they conducted?

For pregnant women with hyperthyroidism syndrome, regular follow-up tests are necessary until thyroid function returns to normal. Depending on the specific situation, thyroid function blood tests are recommended every 2 to 4 weeks.

PREVENTION

Can gestational hyperthyroidism syndrome be prevented?

Currently, there are no effective measures to prevent the occurrence of gestational hyperthyroidism syndrome.

How can patients with gestational hyperthyroidism syndrome prevent complications?

After the onset of gestational hyperthyroidism syndrome, closely monitor changes in the condition and recheck thyroid function every 2–4 weeks based on specific circumstances.

Actively provide symptomatic treatment for emerging symptoms, such as controlling vomiting for hyperemesis gravidarum, correcting dehydration, maintaining energy balance and electrolyte equilibrium, and administering heart rate control as needed for tachycardia. These are effective measures to prevent related complications.