A Royal Thyroid Problem? Severe Morning Sickness and the Thyroid

Patient Expert
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With each of her three pregnancies, Kate Middleton, the Duchess of Cambridge, experienced a complication of pregnancy known as hyperemesis gravidarum. Hyperemesis gravidarum is a condition of early pregnancy that includes severe nausea, vomiting, weight loss, and dehydration. It’s estimated that up to three percent of women suffer from the condition during pregnancy. The cause is not definitive, but it’s thought to be related to elevated hormone levels in pregnancy.

While nausea and vomiting are common during pregnancy — up to half of all pregnant women have some degree of nausea and vomiting — the symptoms of hyperemesis gravidarum are more debilitating, and can include:

  • Prolonged, uncontrolled vomiting
  • An inability to eat or drink without vomiting
  • Significant weight loss of more than 5 percent of your body weight prior to pregnancy
  • Dizziness and fainting
  • Excessive salivation
  • Fatigue

In severe cases, vomiting and failure to eat and drink can lead to dehydration, electrolyte imbalances, and malnutrition, which can slow the baby’s growth. While there is no treatment or cure for the condition, when the vomiting and nausea are severe, some women are prescribed medications. These drugs can include anti-nausea drugs such as metoclopramide (Reglan) and antihistamines to help reduce the symptoms. These medications are generally considered safe for short-term use during pregnancy.

Some women with hyperemesis gravidarum require hospitalization to receive intravenous nutrition and fluid replacement.

Transient hyperthyroidism of hyperemesis gravidarum

A small percentage of hyperemesis gravidarum cases appear to be the result of a thyroid dysfunction during pregnancy. This variation is called transient hyperthyroidism of hyperemesis gravidarum, or THHG. THHG is suspected when in addition to the hyperemesis gravidarum, a pregnant woman also has some symptoms of an overactive thyroid, including:

  • Mild heart palpitations
  • Mild tremor in the hands and fingers
  • Slightly elevated heart rate

Some of the more common hyperthyroidism symptoms such as heat intolerance, sweating, weak muscles, changes to the eyes, and an enlarged thyroid gland (goiter) are not evident in THHG.

When THHG is suspected, thyroid function is typically tested to evaluate for hyperthyroidism, including thyroid stimulating hormone (TSH), free thyroxine (free T4), and thyroid stimulating immunoglobulins (TSI) and or thyroid peroxidase (TPO) antibodies. The goal is to rule out any evidence of autoimmune thyroid disease or significant thyroid dysfunction.

Typically, in THHG, the free T4 levels are elevated, sometimes up to three times the normal value. Free triiodothyronine (free T3) is also typically elevated, but not as much as free T4. The TSH is usually low, in hyperthyroid range. THHG is also characterized by the absence of thyroid antibodies, and no evidence of autoimmunity.

Antithyroid medication is rarely given to treat THHG, except when symptoms are severe and thyroid levels show more significant hyperthyroidism. In that case, a short course of antithyroid drugs may be given.

Typically, by the middle of the second trimester, hyperemesis and THHG resolve. Antithyroid drugs are discontinued at that point. Interestingly, TSH levels may remain low, even as the other thyroid levels return to the normal range.

We don’t know if Kate Middleton had the THHG form of hyperemesis gravidarum during any of her three pregnancies, but her experience offers good news: Despite the extreme discomfort of these conditions, women go on to have healthy babies!

For women suffering from hyperemesis gravidarum or THHG, you can find helpful information at the Hyperemesis Education and Research (HER), located online at www.hyperemesis.org. There is also a helpful Facebook support group online for hyperemesis sufferers.

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