Hypothyroidism During Pregnancy

fatigue
constipation
intolerance to cold
muscle cramps
hair loss
dry skin
carpel tunnel syndrome
weight gain

Dangers to Mother & Fetus with Untreated Hypothyroidism

miscarriage
preeclampsia
prematurity
stillbirth
postpartum hemorrhage

low birth weight
placental abruption
intrauterine growth restriction
congenital cretinism (growth failure,
  mental retardation, deafness, muteness)

Causes of Hypothyroidism

The most common cause of hypothyroidism in pregnancy in the United States is Hashimoto's Thyroiditis. The body produces antibodies against the thyroid gland rendering it unable to manufacture the hormone. However, the most common cause of hypothyroidism world wide is iodine deficiency. Iodine is essential for the manufacture of the hormone.

Other causes include subacute thyroiditis (viral illness of the thyroid gland), certain drugs (ferrous sulfate, phenytoin, rifampin), pituitary or hypothalamic disease, or prior treatment with radioactive iodine to treat Graves Disease.

How is Hypothyroidism Diagnosed?

A blood test is used to detect hypothyroidism. Diagnosis in pregnancy is made by an elevated TSH (thyroid stimulating hormone which is made by the pituitary) and a corresponding low thyroid hormone level (T4).

One can also measure antibody levels in the thyroid hormones (antithyroglobulin, antithyroid peroxidase). Measurement of antibody levels is important because women who have antibodies are at increased risk of pregnancy complications and also increased risk of postpartum thyroid dysfunction. Women can have a goiter or large swelling in the neck area.

Having one autoimmune disease increases the chance of developing another. Women with type I diabetes have a 5 to 8% chance of developing hypothyroidism during pregnancy and a 25% chance of developing postpartum thyroid disease.

How is Hypothyroidism Treated?

The treatment of this disease is to replace the thyroid hormone with levothyroxine till the TSH levels are normal. Generally levels are followed each trimester of the pregnancy since the demands of pregnancy may necessitate an increase in dosage. If the cause of the hypothyroidism is due to iodine deficiency, iodine supplementation is essential not only during pregnancy but also after birth.

Women who take iron during pregnancy due to anemia will have difficulty absorbing their thyroid hormone so these medications should be spaced at least 4 hours apart.

What is Subclinical Hypothyroidism?

This is a subgroup of thyroid impairment found in 2–5% of pregnant women. Generally the T4 is normal but the TSH is elevated. Subclinical hypothyroidism has been linked to faulty placental development. There is a three fold increased risk of abruption, higher miscarriage rate, and a two fold increase in the incidence of preterm birth leading to impaired neurodevelopment in the child.

There is currently a great debate on whether women who present with this condition should be treated since studies have not shown a benefit with replacement. These patients should be followed after delivery because of the increased incidence of developing overt thyroid disease postpartum.

Women with Thyroid Disease Prior to Pregnancy

Pregnancy has a beneficial effect on women with preexisting thyroid disease. Due to the suppression of the immune system, the antibodies found in Hashimoto's disease decline but, immediately postpartum, there can be a resurgence with marked worsening of the condition. There can be a noticeable reduction in goiter size during the pregnancy.

How Does Hypothyroidism Affect your Baby?

Congenital hypothyroidism occurs in one in 4,000 births. There can be multiple etiologies from genetic, immunologic, environmental, and drug induced causes. It is critically important not to miss this diagnosis in the infant since developmental retardation can occur if the condition goes untreated.