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Thyroid Disease in Pregnancy

By Liji Thomas, MD

The thyroid is a master gland at the front of the neck. Small but powerful, it regulates the functioning of most organs and body systems. Deficient functioning of this gland is called hypothyroidism and the opposite condition is called hyperthyroidism. Both can cause serious problems for the mother and the fetus during pregnancy.

Hyperthyroidism Causes

Grave's disease is the most common cause, affecting one in 500 pregnancies. In this autoimmune condition, the body makes antibodies against the thyroid, which have the effect of stimulating it. They are called thyroid-stimulating immunoglobulin (TSI). This causes high levels of thyroid hormone to be produced.

Hypothyroidism Causes

Hashimoto's thyroiditis is the most common cause, about 1 in 1000 pregnancies. Here the body produces antibodies against the thyroid which destroy thyroid cells and enzymes, causing deficiency of thyroid hormone.

Pre-existing hypothyroidism, removal or destruction of the thyroid without proper thyroid hormone replacement in pregnancy are other causes of hypothyroidism in pregnancy.

Hyperthyroidism Symptoms

Symptoms of hyperthyroidism often mimic those of pregnancy itself, and require careful screening to differentiate.

They include:

  • Palpitations and an irregular heartbeat
  • Fast heart rate
  • Extreme persistent tiredness
  • Mild tremors
  • Feeling of heat all the time
  • Jitteriness
  • Excessive nausea or vomiting
  • Insomnia
  • Inadequate weight gain or weight loss

Hypothyroidism Symptoms

Hypothyroidism requires full treatment throughout pregnancy to avoid physical and mental growth retardation of the fetus. For the first 12 weeks of pregnancy the baby receives its thyroid hormone supply from the mother through the placenta. Thereafter the baby's thyroid starts to function independently.

Symptoms include:

  • Sensations of cold
  • Sleepiness and lethargy
  • Swelling over the lower legs
  • Constipation
  • Muscle cramps
  • Poor memory
  • Lack of concentration

Hyperthyroidism Complications

By causing a general acceleration of the body's metabolism, thyroid overactivity can seriously affect the course of pregnancy for both mother and baby. Adverse outcomes include:

  • Miscarriage
  • Fetal or neonatal death
  • Low birth weight
  • High blood pressure
  • Thyroid storm
  • Heart failure

Hypothyroidism Complications

By failing to supply enough thyroid hormone to maintain efficient energy production and regulate vital body processes in the mother and fetus, hypothyroidism is associated with:

  • High blood pressure
  • Anemia
  • Miscarriage
  • Low birth weight
  • Stillbirth
  • Heart failure – rare
  • Mental and physical retardation in the baby, also called cretinism

Diagnosis

Besides the symptoms, physical examination for thyroid swellings and blood work for thyroid hormone levels are usually done. Blood tests measure the levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3) the active form of thyroid hormone and its prohormone, thyroxine (T4), from which T3 is made.

The pregnancy hormones human Chorionic Gonadotropin (hCG) and estrogen affect thyroid hormone levels in blood, making the tests more difficult to interpret. Many pregnant women also have a mild swelling of the thyroid, but without clinical signs or symptoms.

Hyperthyroidism Management

Mild hyperthyroidism doesn't require treatment.

Anti-thyroid drugs are used to suppress excessive thyroid function.

Surgery is used only if drugs are ineffective.

Hypothyroidism Management

Thyroid hormone supplements are used to bring thyroid hormone levels in blood back to normal.

In general, pregnant women need to supplement their diet with multivitamins and iodine to meet their increased needs of many nutrients. However, in some cases of thyroid disease, iodine triggers worsening of the condition. All supplements should be discussed with the healthcare provider before starting their use.

Last Updated: Mar 11, 2015

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