Thyroid Disease in Pregnancy


During pregnancy, abnormal thyroid function can harm the mother and the developing fetus. Thyroid hormone is essential to the development of the fetal brain and nervous system. Until about 12 weeks gestation, the fetus depends on its mother’s thyroid hormone, which crosses the placenta freely.

A placental hormone active during pregnancy, human chorionic gonadotropin (hCG), increases the secretion of thyroid hormones. This causes the usual stimulating hormone, TSH, to fall substantially in the first trimester of pregnancy. Since TSH is our most sensitive marked for thyroid disease, this makes thyroid disorders difficult to diagnose in pregnancy. Women who have a personal or family history of thyroid disease should be carefully monitored.

Types Of Thyroid Disease During Pregnancy

There are two primary types of thyroid disease that occur during pregnancy: hyperthyroidism and hypothyroidism. Either disorder, although diagnosed during pregnancy, may have been a pre-existing condition.


Hyperthyroidism occurs if the thyroid is too active, producing excessive levels of thyroid hormones. During pregnancy, hyperthyroidism is usually caused by Graves’ disease, an autoimmune condition. Symptoms of hyperthyroidism may include:

  • Hyperactivity, nervousness, irritability
  • Rapid or irregular heartbeat
  • Increased sensitivity to heat
  • Excessive sweating
  • More frequent bowel movements
  • Weight loss or failure to gain normal pregnancy weight
  • Muscle weakness
  • Insomnia
  • Eye bulging or irritation

Patients with Graves’ disease may develop hyperemesis gravidarum, resulting in severe nausea and vomiting.


Hypothyroidism is the condition of an underactive thyroid. During pregnancy, hypothyroidism is typically caused by Hashimoto’s disease, an autoimmune disorder that causes chronic inflammation of the thyroid gland. Symptoms of hypothyroidism during pregnancy may include:

  • Excessive weight gain
  • Constipation
  • Increased sensitivity to cold
  • Dry skin
  • Hoarseness
  • Depression
  • Joint and muscle aches
  • Muscle weakness

Complications Of Thyroid Disease During Pregnancy

It is essential that thyroid disease be controlled during pregnancy. Untreated it may result in several serious risks to the mother or newborn, including:

  • Anemia
  • Preeclampsia
  • Heart failure
  • Miscarriage or premature birth
  • Low birth weight, poor weight gain
  • Early closure of the fontanelles (the soft spots in the infant’s skull)

Diagnosis Of Thyroid Disease During Pregnancy

Both hyperthyroidism and hypothyroidism are diagnosed during pregnancy by assessing physical symptoms, administering thyroid function tests, and taking blood tests to measure hormone levels. Because of the thyroid-stimulating effects of hCG, more complex blood testing is required in the pregnant patient.

Treatment Of Thyroid Disease During Pregnancy

Pregnant patients with hyperthyroidism may be treated with a medication to slow production of thyroid hormones and will be required to restrict their dietary intake of iodine.

Pregnant patients with hypothyroidism are treated with thyroid hormone in order to restore proper levels of thyroid hormone.

Robert Howe, MD

281 Maple St.
East Longmeadow, MA 01028

Tel: (413) 525-5160
Fax: (413) 525-5170

Mon-Fri: 8:00am – 5:00pm
Saturday: 8:00am – 12:00pm

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